NCERT Solutions Class 7th Math Chapter – 2 Fractions and Decimals Exercise – 2.4

1. Find:

(i) 0.2 × 6

Solution:

We have,
= (2/10) × 6
= (12/10)
On dividing a decimal by 10, the decimal point is shifted to the left by one place.
Then,
= 1.2

(ii) 8 × 4.6

Solution:

We have,
= (8) × (46/10)
= (368/10)
On dividing a decimal by 10, the decimal point is shifted to the left by one place.
Then,
= 36.8

(iii) 2.71 × 5

Solution:

We have,
= (271/100) × 5
= (1355/100)
On dividing a decimal by 100, the decimal point is shifted to the left by two places.
Then,
= 13.55

(iv) 20.1 × 4

Solution:

We have,
= (201/10) × 4
= (804/10)
On dividing a decimal by 10, the decimal point is shifted to the left by one place.
Then,
= 80.4

(v) 0.05 × 7

Solution:

We have,
= (5/100) × 7
= (35/100)
On dividing a decimal by 100, the decimal point is shifted to the left by two places.
Then,
= 0.35

(vi) 211.02 × 4

Solution:

We have,
= (21102/100) × 4
= (84408/100)
On dividing a decimal by 100, the decimal point is shifted to the left by two places.
Then,
= 844.08

(vii) 2 × 0.86

Solution:

We have,
= (2) × (86/100)
= (172/100)
On dividing a decimal by 100, the decimal point is shifted to the left by two places.
Then,
= 1.72

2. Find the area of rectangle whose length is 5.7cm and breadth is 3 cm.

Solution:

From the question, it is given that,
Length of the rectangle = 5.7 cm
Breadth of the rectangle = 3 cm

Then,
Area of the rectangle = length × Breadth
= 5.7 × 3
= 17.1 cm²

3. Find:

(i) 1.3 × 10

Solution:

On multiplying a decimal by 10, the decimal point is shifted to the right by one place.
We have,
= 1.3 × 10 = 13

(ii) 36.8 × 10

Solution:

On multiplying a decimal by 10, the decimal point is shifted to the right by one place.
We have,
= 36.8 × 10 = 368

(iii) 153.7 × 10

Solution:

On multiplying a decimal by 10, the decimal point is shifted to the right by one place.
We have,
= 153.7 × 10 = 1537

(iv) 168.07 × 10

Solution:

On multiplying a decimal by 10, the decimal point is shifted to the right by one place.
We have,
= 168.07 × 10 = 1680.7

(v) 31.1 × 100

Solution:

On multiplying a decimal by 100, the decimal point is shifted to the right by two places.
We have,
= 31.1 × 100 = 3110

(vi) 156.1 × 100

Solution:

On multiplying a decimal by 100, the decimal point is shifted to the right by two places.
We have,
= 156.1 × 100 = 15610

(vii) 3.62 × 100

Solution:

On multiplying a decimal by 100, the decimal point is shifted to the right by two places.
We have,
= 3.62 × 100 = 362

(viii) 43.07 × 100

Solution:

On multiplying a decimal by 100, the decimal point is shifted to the right by two places.
We have,
= 43.07 × 100 = 4307

(ix) 0.5 × 10

Solution:

On multiplying a decimal by 10, the decimal point is shifted to the right by one place.
We have,
= 0.5 × 10 = 5

(x) 0.08 × 10

Solution:

On multiplying a decimal by 10, the decimal point is shifted to the right by one place.
We have,
= 0.08 × 10 = 0.8

(xi) 0.9 × 100

Solution:

On multiplying a decimal by 100, the decimal point is shifted to the right by two places.
We have,
= 0.9 × 100 = 90

(xii) 0.03 × 1000

Solution:

On multiplying a decimal by 1000, the decimal point is shifted to the right by three places.
We have,
= 0.03 × 1000 = 30

4. A two-wheeler covers a distance of 55.3 km in one litre of petrol. How much distance will it cover in 10 litres of petrol?

Solution:

From the question, it is given that,
Distance covered by two-wheeler in 1L of petrol = 55.3 km

Then,
Distance covered by two wheeler in 10L of petrol = (10 × 55.3)
= 553 km

∴ Two-wheeler covers a distance in 10L of petrol is 553 km.

5. Find:

(i) 2.5 × 0.3

Solution:

We have,
= (25/10) × (3/10)
= (75/100)
On dividing a decimal by 100, the decimal point is shifted to the left by two places.
Then,
= 0.75

(ii) 0.1 × 51.7

Solution:

We have,
= (1/10) × (517/10)
= (517/100)
On dividing a decimal by 100, the decimal point is shifted to the left by two places.
Then,
= 5.17

(iii) 0.2 × 316.8

Solution:

We have,
= (2/10) × (3168/10)
= (6336/100)
On dividing a decimal by 100, the decimal point is shifted to the left by two places.
Then,
= 63.36

(iv) 1.3 × 3.1

Solution:

We have,
= (13/10) × (31/10)
= (403/100)
On dividing a decimal by 100, the decimal point is shifted to the left by two places.
Then,
= 4.03

(v) 0.5 × 0.05

Solution:

We have,
= (5/10) × (5/100)
= (25/1000)
On dividing a decimal by 1000, the decimal point is shifted to the left by three places.
Then,
= 0.025

(vi) 11.2 × 0.15

Solution:

We have,
= (112/10) × (15/100)
= (1680/1000)
On dividing a decimal by 1000, the decimal point is shifted to the left by three places.
Then,
= 1.68

(vii) 1.07 × 0.02

Solution:

We have,
= (107/100) × (2/100)
= (214/10000)
On dividing a decimal by 10000, the decimal point is shifted to the left by four places.
Then,
= 0.0214

(viii) 10.05 × 1.05

Solution:

We have,
= (1005/100) × (105/100)
= (105525/10000)
On dividing a decimal by 10000, the decimal point is shifted to the left by four places.
Then,
= 10.5525

(ix) 101.01 × 0.01

Solution:

We have,
= (10101/100) × (1/100)
= (10101/10000)
On dividing a decimal by 10000, the decimal point is shifted to the left by four places.
Then,
= 1.0101

(x) 100.01 × 1.1

Solution:

We have,
= (10001/100) × (11/10)
= (110011/1000)
On dividing a decimal by 1000, the decimal point is shifted to the left by three places.
Then,
= 110.011