RS Aggarwal 2019,2020 solution class 7 chapter 3 Decimals Exercise 3E

Exercise 3E

Page-51

Question 10:

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What should be added to 3.07 to get 3.5?

(a) .57
(b) .34
(c) .43
(d) .02

Answer 10:

(c) .43
We have:
3.07 + x = 3.5
⇒ x = 3.5 − 3.07
Converting the given decimals into like decimals, we get:
3.07 and 3.50
Writing them in column form with the larger one at the top and subtracting, we get:

∴ x  = 0.43

Hence, 0.43 should be added to 3.07 to get 3.5.

Question 11:

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0.23 × 0.3 = ?

(a) 0.69
(b) 6.9
(c) 0.069
(d) none of these

Answer 11:

(c) 0.069
First, we will multiply 23 by 3.
i.e., 23 $\times$ 3 = 69
Sum of decimal places in the given decimals  = (2 + 1) = 3
∴ 0.23 $\times$ 0.3 = 0.069     ( 3 places of decimal)

Question 12:

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0.02 × 30 = ?

(a) 6
(b) 0.6
(c) 0.06
(d) none of these

Answer 12:

(b) 0.6
We have:
2 $\times$ 30 = 60
∴ 0.02 $\times$ 30 = 0.60            (2 places of decimal)
                        = 0.6

Question 13:

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0.25 × 0.8 = ?

(a) 0.02
(b) 0.2
(c) 0.002
(d) 2

Answer 13:

(b) 0.2
First, we will multiply 25 by 8.
∴ 25 $\times$ 8 = 200
Sum of decimal places in the given decimals = (2 + 1) = 3
∴ 0.25 $\times$ 0.8 = 0.200    [3 places of decimal]
                        = 0.2

Question 14:

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0.4 × 0.4 × 0.4 = ?

(a) 6.4
(b) .64
(c) .064
(d) none of these

Answer 14:

(c) .064

First, we will find the product 4 $\times$ 4 $\times$ 4 = 64
Sum of decimal places in the given decimals = (1 + 1 + 1) = 3
∴ 0.4 × 0.4 × 0.4 = 0.064   ( 3 places of decimal)

Question 15:

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1.1 × .1 ×.01 = ?

(a) .011
(b) .0011
(c) .11
(d) none of these

Answer 15:

(b) .0011

First, we will find the product 11 $\times$ 1 $\times$ 1.
Sum of decimal places in the given decimals  = (1 + 1 + 2) = 4
∴ 1.1 $\times$  0.1 $\times$ 0.01 = 0.0011   (4 places of decimal)

Question 16:

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2.08 ÷ (.16) = ?

(a) 13
(b) .13
(c) 1.3
(d) none of these

Answer 16:

(a) 13

2.08 ÷ 0.16 = $\frac{2.08}{0.16}$ = $\frac{2.08\times 100}{0.16\times 100}$ = $\frac{208}{16}=13$

Question 17:

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1.02 ÷ 6 = ?

(a) 1.7
(b) 0.17
(c) 0.017
(d) none of these

Answer 17:

(b) 0.17

1.02 ÷ 6 = $\frac{1.02}{6}=\frac{1.02\times 100}{6\times 100}=\frac{102}{6\times 100}=\frac{17}{100}=0.17$

Question 18:

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30.94 ÷ 0.7 = ?

(a) 44.2
(b) 4.42
(c) 442
(d) 0.442

Answer 18:

(a) 44.2

30.94 ÷ 0.7 = $\frac{30.94}{0.7}=\frac{30.94\times 100}{0.7\times 100}=\frac{3094}{70}=44.2$

Question 19:

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2.73 ÷ 1.3 = ?

(a) 21
(b) 2.1
(c) 0.21
(d) none of these

Answer 19:

(b) 2.1

2.73 ÷ 1.3 = $\frac{2.73}{1.3}= \frac{2.73\times 100}{1.3\times 100} = \frac{273}{13\times 10} = \frac{21}{10} = 2.1$

Question 20:

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89.1 ÷ 2.2 = ?

(a) 40.5
(b) 4.05
(c) 41
(d) 41.5

Answer 20:

(a) 40.5

89.1 ÷ 2.2 = $\frac{89.1}{2.2} = \frac{89.1 \times 10}{2.2 \times 10} = \frac{891}{22} = 40.5$

Question 21:

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0.5 × 0.05 = ?

(a) 0.25
(b) 2.5
(c) 0.025
(d) none of these

Answer 21:

(c) 0.025
First, we will multiply 5 by 5.
i.e., 5 $\times$ 5 = 25
Sum of decimal places in the given decimals = (1 + 2) = 3
∴ 0.5 × 0.05 = 0.025   (3 places of decimal)