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Textbook page 7
Textbook page 7 · solved item 1

Recall that a tenth is 0.1, a hundredth is 0.01, and so on. Find the following products in tenths, hundredths, and so on: (a) 6 × 4 tenths = 24 tenths (b) 7 × 0.3 (c) 9 × 5 hundredths
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(a) Here, 6 × 4 tenths = 24 tenths. (b) 7 × 0.3 = 7 × 3 tenths = 21 tenths (c) Here, 9 × 5 hundredths = 45 hundredths
Textbook page 7 · solved item 2

Find the products: (a) 27.34 × 6 (b) 4.23 × 3.7 (c) 0.432 × 0.23
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(a) 27.34 × 6 = 164.04. (b) 4.23 × 3.7 = 15.651. (c) 0.432 × 0.23 = 0.09936.
Textbook page 7 · solved item 3

Thejus needs 1.65 m of cloth for a shirt. How many metres of cloth are needed for 3 shirts?
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Given: Thejus needs 1.65 m of cloth for a shirt. For 3 shirts, the total cloth needed = 1.65 × 3 = \frac {165}{100} × 3 = \frac {495}{100} = 4.95
Textbook page 7 · solved item 4

Meenu bought 4 notebooks and 3 erasers. The cost of each book was ₹ 15.50, and each eraser was ₹ 2.75. How much did she spend in all?
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Here cost of 1 notebook = ₹ 15.50 Therefore, Cost of 4 notebooks = 4 × 15.50 = \frac{4 \times 1550}{100} = \frac {6200}{100} = ₹ 62 and cost of 1 eraser = ₹ 2.75 Therefore, Cost of 3 erasers = 3 × ₹ 2.75 = \frac{3 \times 275}{100} = \frac {825}{100} = ₹ 8.25 Therefore, Total amount spent = 62 + 8.25 = ₹ 70.25
Textbook page 7 · solved item 5

The thickness of a rupee coin is 1.45 mm. What is the total height of the cylinder formed by placing 36 rupee coins one over the other? Write the answer in centimetres.
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Thickness of 1 coin = 1.45 mm Total thickness of 36 coins = 36 × 1.45 = \frac{36 \times 145}{100} = \frac {5220}{100} = 52.2 mm Now 10 mm = 1 cm 1 mm = \frac {1}{10} cm Therefore, 52.2 mm = \frac {52.2}{10} = 5.22 cm.
Textbook page 7 · solved item 6

The price of 1 kg of oranges is ₹ 56.50. What is the price of 2.250 kg of oranges? Can we write 56.50 as 56.5 and 2.250 as 2.25 and multiply? Will we get the same product? Why?
Show solution
Price of 1 kg of oranges = ₹ 56.50 Price of 2.250 kg of oranges = 56.50 × 2.250 = \frac{5650 \times 2250}{100 \times 1000} = \frac {12712500}{100000} = ₹ 127.125 Now 56.5 × 2.25 = 127.125 Hence, we will get the same product. The zeroes at the end of a decimal do not change its value. As we saw, 56.50 is the same as 56.5, and 2.250 is the same as 2.25.
Hence, the product of the two numbers will be the same.
Textbook page 7 · solved item 7

Dwarakanath purchases notebooks at a wholesale price of ₹ 23.6 per piece and sells each notebook at ₹ 30/-. How much profit does he make if he sells 50 books in a week?
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Profit per notebook = Selling price – wholesale price = 30 – 23.6 = ₹ 6.4 Total profit = Profit per notebook × No. of notebooks = 6.4 × 50 = ₹ 320
Textbook page 7 · solved item 8

Given that 18 × 12 = 216, find the products: (a) 18 × 1.2 (b) 18 × 0.12 (c) 1.8 × 1.2 (d) 0.18 × 0.12 (e) 0.018 × 0.012 (f) 1.8 × 12 In which of the cases above is the product less than 1?
Show solution
(a) Here 18 × 12 = 216 …..(i) Now 18 × 1.2 = \frac{18 \times 12}{10} [Using (i)] = \frac {216}{10} = 21.6 (1 decimal place) (b) 18 × 0.12 = \frac{18 \times 12}{100} (Using (i)) = \frac {216}{100} = 2.16 (2 decimal places) (c) 1.8 × 1.2 = \frac{18}{10} \times \frac{12}{10}=\frac{216}{100} [Using (i)] = 2.16 (2 decimal places) (d) 0.18 × 0.12 = \frac{18}{100} \times \frac{12}{100}=\frac{216}{100 \times 100} [Using (i)] = 0.0216 (4 decimal places) (e) 1.8 × 12 = \frac{18 \times 12}{10}=\frac{216}{10} [Using (i)] = 21.6 (1 decimal place) When multiplying two numbers positive if both numbers are less than 1, their product will also be less than 1.
In (d) and (e) product is less than 1.
Textbook page 7 · solved item 9

In which of the following multiplications is the product less than 1? Can you find the answer without actually doing the multiplications? (a) 7 × 0.6 (b) 0.7 × 0.6 (c) 0.7 × 6 (d) 0.07 × 0.06
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Yes, we can find the answer without actual multiplication, only by using decimal place values. Multiplying by a number greater than 1: The product is greater than the original number. Multiplying by a number between 0 and 1: The product is less than the original number. Multiplying two numbers between 0 and 1: The product will be less than both factors, and therefore definitely less than 1.
(a) Greater than 1. (b) Less than 1. (c) Greater than 1. (d) Less than 1.
Textbook page 7 · solved item 10

Multiplying the following numbers by 10, 100, and 1000 to complete the table.
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Completed table: 5.7 gives 57, 570, 5700; 23.02 gives 230.2, 2302, 23020; 0.92 gives 9.2, 92, 920; 0.306 gives 3.06, 30.6, 306; and 24.67 gives 246.7, 2467, 24670 when multiplied by 10, 100, and 1000 respectively.
Complete worked answers
Textbook page 17
Textbook page 17 · solved item 11

Find the quotient by converting the denominator into 1, 10, 100, or 1000 and verify the solution by the long division method (division by place value). (a) \frac {18}{5} (b) \frac {415}{4} (c) \frac {1217}{2} (d) \frac {4827}{8}
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(a) Given \frac {18}{5} To convert the denominator 5 into 10, multiply both the numerator and Dr by 2. \frac{18 \times 2}{5 \times 2}=\frac{36}{10} = 3.6 Verification 18 ÷ 5 Dividing 1 ten and 8 ones into 5 equal parts. 1 < 5 It means we need to regroup 1 ten as 10 ones, i.e., 10 + 8 = 18 ones 18 ones ÷ 5 3 ones remain.
To divide 3 ones into 5 equal parts. Regroup the 3 ones as 30 Tenths. (Place a decimal while regrouping ones into tenths). 30 Tenths ÷ 5 = 6 Then, 18 ÷ 5 = 3.6 Hence verified. (b) Given \frac {415}{4} To convert the denominator 4 into 100, multiply both the Nr and Dr by 25. \frac{415 \times 25}{4 \times 25}=\frac{10375}{100} = 103.75 Verification By following the steps Therefore, 414 ÷ 4 = 103.75 Hence verified.
(c) Given \frac {1217}{2} To convert the denominator 2 into 10, multiply both the Nr and Dr by 5. \frac{1217 \times 5}{2 \times 5}=\frac{6085}{10} = 608.5 Verification By following the steps: Therefore, 1217 ÷ 2 = 608.5 Hence verified. (d) Given \frac {4827}{8} To convert the denominator 8 into 1000, multiply both the Nr and Dr by 125. \frac{4827 \times 125}{8 \times 125}=\frac{603375}{1000} = 603.375 Verification By following the steps: We get 4827 ÷ 8 = 0603.375 Hence verified.
Textbook page 17 · solved item 12

Choose the correct answer: (a) \frac {1526}{4} = _____ (i) 38.15 (ii) 380.15 (iii) 381.5 (iv) 381.05 (b) \frac {3567}{8} = _____ (i) 4458.75 (ii) 44.5875 (iii) 445.875 (iv) 4458.75
Show solution
(a) \frac {1526}{4} By using the Long Division Method: Hence, option (iii) is correct. (b) Given \frac {3567}{8} By using the Long Division Method: Hence, option (iii) is correct.
Textbook page 17 · solved item 13

What is the quotient? (a) 132 ÷ 4 = _____ (b) 13.2 ÷ 4 = _____ (c) 1.32 ÷ 4 = _____ (d) 0.132 ÷ 4 = _____
Show solution
(a) \frac {132}{4} Therefore, Quotient = 33 (b) \frac {13.2}{4} = \frac {132}{40} Therefore, Quotient = 3.3 (c) Here \frac{1.32}{4}=\frac{132}{400} Therefore, Quotient = 0.33 (d) Here \frac{0.132}{4}=\frac{132}{4000} Therefore, Quotient = 0.033
Textbook page 17 · solved item 14

What is the quotient? (a) 126 ÷ 8 = _____ (b) 12.6 ÷ 8 = _____ (c) 1.26 ÷ 8 = _____ (d) 0.126 ÷ 8 = _____ (e) 0.0126 ÷ 8 = _____
Show solution
(a) \frac {126}{8} Hence quotient = 15.75 (b) \frac {12.6}{8} Hence quotient = 1.575 (c) Here 1.26 ÷ 8 Hence quotient = 0.1575 (d) Here 0.126 ÷ 8 Hence quotient = 0.01575 (e) Here 0.0126 ÷ 8 Hence quotient = 0.001575
Complete worked answers
Textbook page 20
Textbook page 20 · solved item 15

Express the following fractions in decimal form: (a) \frac {2}{5} (b) \frac {13}{4} (c) \frac {4}{50} (d) \frac {5}{8}
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(a) \frac {2}{5} Multiply both the Nr and Dr by 2. \frac{2}{5} \times \frac{2}{2}=\frac{4}{10} Now, put decimal \frac {4}{10} = 0.4 Hence \frac {2}{5} in decimal form is 0.4. (b) \frac {13}{4} Multiply both the Nr and Dr by 25. \frac{13}{4} \times \frac{25}{25}=\frac{325}{100} Now, put a decimal \frac {325}{100} = 3.25 Hence \frac {13}{4} in decimal form is 3.25.
(c) \frac {4}{50} Multiply both the Nr and Dr by 2. \frac{4}{50} \times \frac{2}{2}=\frac{8}{100} Now, put the decimal \frac {8}{100} = 0.08 Hence \frac {4}{50} in decimal form is 0.08. (d) \frac {5}{8} Multiply both the Nr and Dr by 125. \frac{5}{8} \times \frac{125}{125}=\frac{625}{1000} Now, put the decimal \frac {625}{1000} = 0.625 Hence \frac {5}{8} in decimal form is 0.625.
Textbook page 20 · solved item 16

Find the quotients: (a) 24.86 ÷ 1.2 (b) 5.728 ÷ 1.52
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(a) Here 24.86 ÷ 1.2 Converting division into a fraction, we get \frac{24.86}{1.2}=\frac{2486 \times 10}{12 \times 100}=\frac{2486}{120} Now Therefore, Quotient = 20.7166… (b) Converting division into a fraction, we get Therefore, Quotient = 3.76
Complete worked answers
Textbook page 21
Textbook page 21 · solved item 17

Evaluate the following using the information 156 × 12 = 1872. (a) 15.6 × 1.2 = _____ (b) 187.2 ÷ 1.2 = _____ (c) 18.72 ÷ 15.6 = _____ (d) 0.156 × 0.12 = _____
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Given 156 × 12 = 1872 ……(i) ⇒ 156 = \frac {1872}{12} …….(ii) ⇒ 12 = \frac {1872}{156} …….(iii) (a) Now converting division into a fraction 15.6 × 1.2 = \frac{156 \times 12}{10 \times 10}=\frac{1872}{100} = 18.72 [using (i)] (b) Converting division into a fraction 187.2 ÷ 1.2 187.2 ÷ 1.2 = \frac{187.2}{1.2}=\frac{1872}{12} = 156 [using (ii)] (c) Converting division into a fraction 18.72 ÷ 15.6, we get 18.72 ÷ 15.6 = \frac{18.72}{15.6}=\frac{1872 \times 10}{156 \times 100} = \frac {12}{10} = 1.2 [Using (iii)] (d) Here 0.156 × 0.12 = \frac{156 \times 12}{1000 \times 100} [Using (i)] = \frac{1872}{1000 \times 100} = 0.01872
Textbook page 21 · solved item 18

Evaluate the following: (a) 25 ÷ _____ = 0.025 (b) 25 ÷ _____ = 250 (c) 25 ÷ _____ = 2.5 (d) 25 ÷ 10 = 25 × _____ (e) 25 ÷ 0.10 = 25 × _____ (f) 25 ÷ 0.01 = 25 × _____
Show solution
(a) 1000, because 25 ÷ 1000 = 0.025. (b) 0.1. (c) 10. (d) 0.1. (e) 10. (f) 100.
Textbook page 21 · solved item 19

Find the quotients: (a) 2.46 ÷ 1.5 = _____ (b) 2.46 ÷ 0.15 = _____ (c) 2.46 ÷ 0.015 = _____ Is the quotient obtained in 24.6 ÷ 1.5 the same as the quotient obtained in 2.46 ÷ 0.15?
Show solution
Converting 2.46 ÷ 1.5 into fraction \frac{2.46}{1.5}=\frac{246 \times 10}{15 \times 100}=\frac{246}{150} Therefore, Quotient = 1.64 (b) Converting 2.46 ÷ 0.15 into a fraction, we get \frac{2.46}{0.15}=\frac{246 \times 100}{15 \times 100}=\frac{246}{15} Therefore, Quotient = 16.4 (c) Converting 2.46 ÷ 0.015 into a fraction, we get \frac{2.46}{0.015}=\frac{246 \times 1000}{15 \times 100}=\frac{2460}{15} Therefore, Quotient = 164 Now \frac{24.6}{1.5}=\frac{246 \times 10}{15 \times 10}=\frac{246}{15} and \frac{2.46}{0.15}=\frac{246 \times 100}{15 \times 100}=\frac{246}{15} Both are the same.
Hence quotient obtained in 24.6 ÷ 1.5 is the same as the quotient obtained in 2.46 ÷ 0.15.
Textbook page 21 · solved item 20

A 4 m long wooden block has to be cut into 5pieces of equal length. What is the length of each piece?
Show solution
Here total length = 4 m No. of pieces = 5 Length of each piece = \frac{\text { Total length }}{\text { No. of pieces }} = \frac {4}{5} = 0.8 m
Textbook page 21 · solved item 21

If the perimeter of a regular polygon with 12 sides is 208.8 cm, what is the length of its side?
Show solution
Here Perimeter = 208.8 cm No. of sides = 12 Length 0f a side = \frac{\text { Perimeter }}{\text { No. of sides }} = \frac {208.8}{12} = 17.4 cm
Textbook page 21 · solved item 22

3 litres of watermelon juice is shared among 8 friends equally. How much watermelon juice will each get? Express the quantity of juice in millilitres.
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Here total quantity of juice = 3 litres No. of friends = 8 Therefore, Juice per friend = \frac {3}{8} litre = \frac {3}{8} × 1000 ml = \frac {3000}{8} = 375 ml
Textbook page 21 · solved item 23

A car covers 234.45 km using 12.6 litres of petrol. What is the distance travelled per litre?
Show solution
Given total distance = 234.45 km Total petrol = 12.6 litres Hence, the total distance travelled per litre of petrol is 18.607 km.
Textbook page 21 · solved item 24

13.5 kg of flour (aata) was distributed equally among 15 students. How much flour did each student receive?
Show solution
Total quantity of flour = 13.5 kg No. of students = 15 Flour per student = \frac {13.5}{15} = 0.9 kg Now Each student receives = 0.9 kg.
Complete worked answers
Textbook page 27
Textbook page 27 · solved item 25

A 210-gram packet of peanut chikki costs ₹ 70.5, while a 110-gram packet of potato chips costs ₹ 33.25. Which is cheaper?
Show solution
Given cost of a peanut is ₹ 70.5 per 210 grams. Therefore, Cost per gram = \frac {70.5}{210} = 0.3357 and cost of potato chips is ₹ 33.25 for 110 grams. Therefore, Cost per gram = \frac {33.25}{110} = 0.3023 because 0.3023 < 0.3357. Hence, potato chips are cheaper.
Textbook page 27 · solved item 26

Write the decimal number at the arrow mark:
Show solution
(i) Here number line is divided into 10 equal parts. Difference between 3.2 and 3.1 = 3.2 – 3.1 = 0.1 Value of each mark = \frac {0.1}{10} = 0.01 Now the arrow is on the sixth mark after 3.1 Therefore, Decimal number at the arrow mark = 3.1 + 6 × 0.01 = 3.1 + 0.06 = 3.16 (ii) Here number line is divided into 10 equal parts between 2.15 and 2.17.
Therefore, Difference between 2.17 and 2.15 = 2.17 – 2.15 = 0.02 Value of each mark = \frac {0.02}{10} = 0.002 Arrow is on the sixth mark after 2.15 Therefore, Decimal number at the arrow mark = 2.15 + 6 × 0.002 = 2.150 + 0.012 = 2.162
Textbook page 27 · solved item 27

Shyamala bought 3 kg of bananas at ₹ 30/- per kg. She counted 35 bananas in all. She sells each banana for ₹ 5/-. How much profit does she make selling all the bananas?
Show solution
Given that Shyamala bought 3 kg of bananas at ₹ 30 per kg. Total cost = 3 × 30 = ₹ 90 She sold 35 bananas for ₹ 5 each. Total revenue = 35 × 5 = ₹ 175 Profit = Total revenue – Total cost = 175 – 90 = ₹ 85
Textbook page 27 · solved item 28

A teacher placed textbooks that are 2.5 cm thick on a bookshelf. The teacher wanted to place 80 textbooks on the shelf. The bookshelf is 160 cm long. How many books could be placed on the shelf? Was there any space left? If yes, how much?
Show solution
Given that, the teacher wanted to place 80 textbooks, each is 2.5 cm thick. Total thickness required = 80 × 2.5 = 200 cm The bookshelf is 160 cm long. The thickness of one book is 2.5 cm. Number of books that can fit = \frac{160 \mathrm{~cm}}{2.5 \mathrm{~cm}} = 64 64 books could be placed on the shelf.
The total thickness of these books = 64 × 2.5 = 160 cm, which is the full length of the shelf. The teacher wanted to place 80 textbooks, but only 64 textbooks can fit. Therefore, there is no space left after placing the maximum number of books.
Complete worked answers
Textbook page 28
Textbook page 28 · solved item 29

Fill in the following blanks appropriately:
Show solution
Here, (i) 1 km = 1000 m Therefore, 5.5 km = 5.5 × 1000 = 5500 m (ii) 1 m = 100 cm Therefore, 35 cm = \frac {35}{100} = 0.35 m (iii) 1 cm = 10 mm Therefore, 14.5 cm = 14.5 × 10 = 145 mm (iv) 1 kg = 1000 g Therefore, 68 g = \frac {68}{1000} = 0068 kg (v) 1 m = 1000 mm Therefore, 9.02 m = 9.02 × 1000 = 9020 mm (vi) 1 l = 1000 ml Therefore, 125.5 ml = \frac {125.5}{1000} = 0.1255 l
Textbook page 28 · solved item 30

The following problem was set by Sridharacharya in his book, Patiganita. “6\frac {1}{4} is divided by 2\frac {1}{2}, and 60\frac {1}{4} is divided by 3\frac {1}{2}. Tell the quotients separately.” Can you try to solve by converting the fractions into decimals?
Show solution
Therefore, Quotient = 17.21
Textbook page 28 · solved item 31

Fill the boxes in at least 2 different ways:
Show solution
(a) Here 1.2 × 2 = 2.4 and 0.4 × 6 = 2.4 (b) Here 2.9 × 5 = 14.5 and 14.5 × 1 = 14.5
Textbook page 28 · solved item 32

Find the following quotients given that 756 ÷ 36 = 21: (a) 75.6 ÷ 3.6 (b) 7.56 ÷ 0.36 (c) 756 ÷ 0.36 (d) 75.6 ÷ 360 (e) 7560 ÷ 3.6 (f) 7.56 ÷ 0.36
Show solution
(a) 21. (b) 21. (c) 2100. (d) 0.21. (e) 2100. (f) 21. These follow by shifting both dividend and divisor by the same power of 10 before using 756 ÷ 36 = 21.
Textbook page 28 · solved item 33

Find the missing cells if each cell represents a ÷ b:
Show solution
Here table given here represents division, where the value in each cell is the result of dividing the number in the corresponding ‘a’ column b the number in the corresponding row ‘b’. Given 1517 ÷ 37 = 41 \frac {151.7}{3.7} = 41 \frac {15.17}{0.37} = 41 \frac {1.517}{37} = 0.041
Textbook page 28 · solved item 34

Using the digits 2, 4, 5, 8, and 0, fill the boxes to get the: (a) maximum product (b) minimum product (c) product greater than 150 (d) product nearest to 100 (e) product nearest to 5
Show solution
One valid set is: (a) maximum product, 82.0 × 5.4 = 442.8; (b) minimum product, 45.8 × 0.2 = 9.16; (c) a product greater than 150, 85.4 × 2.0 = 170.8; (d) product nearest to 100, 20.5 × 4.8 = 98.4; (e) product nearest to 5, 45.8 × 0.2 = 9.16.
Complete worked answers
Textbook page 29
Textbook page 29 · solved item 35

Sort the following expressions in increasing order: (a) 245.05 × 0.942368 (b) 245.05 × 7.9682 (c) 245.05 ÷ 7.9682 (d) 245.05 ÷ 0.942368 (e) 245.05 (f) 7.9682
Show solution
Let A = 245.05, B = 0.942368, C = 7.9682 We note that B < 1 and C > 1 (a) Now A × B = 245.05 × 0.942368 < 245.05 (Therefore, Multiplying a number by a value less than 1 results in a smaller number) (b) A × C = 245.05 × 7.9682 > 245.05 (Multiplying a number by a value greater than 1 results in a larger number) (c) A ÷ C = 2.4505 ÷ 7.9682 < 245.05 (Dividing a number by a value greater than 1 results in a smaller number) (d) A ÷ B = 245.05 ÷ 0.942368 > 245.05 (Dividing a number by a value greater than 1 results in a larger number) (e) Now, expression less than 245.05 Therefore, 0.942368 is closer to 1 than 7.9682 is to 1.
0.942368 will result in a value closer to 245.05 than dividing by 7.9682. Therefore, (c) < (a) Again, 0.942368 is closer to 1 than 7.9682 is to 1. Therefore, Dividing by 0.942368 will result in a value closer to 245.05 than multiplying by 7.9682. Therefore, (d) < (b) Also, (f) 7.9682 is significantly smaller than 245.05; it will be the smallest value.
(f) Therefore, 7.9682 < (e) 245.05 ÷ 7.9682 Combining all, we get (f), (c), (a), (e),(d), (b).
