Selina Concise Class 7 Math Chapter 6 Ratio And Proportion Exercise 6B Solution

Selina Concise Class 7 Math Chapter 6 Ratio And Proportion Exercise 6B Solution

EXERCISE 6B

(1) Check whether the following quantities form a proportion or not:

(i) 3x × 56 = 7x × 24

⇒ 168x = 168x

Hence, the given four quantities are in proportion.

(ii) 0.8 × 9 = 3 × 2.4

⇒ 7.2 = 7.2

Hence, the given four quantities are in proportion.

Hence, the given four quantities are in proportion.

(iv) 0.4 × 3.5 = 0.5 × 2.9

⇒ 1.4 ≠ 1.45

Hence, the given four quantities are not in proportion.

Hence, the given four quantities are not in proportion.

(2) Find the fourth proportional of:

Let the fourth proportion is x.

(v) 4 hours 40 mins = (4 × 60) + 40 = 280 minutes

1 hour 10 mins = 60 + 10 = 70 minutes

16 hours = (16 × 60) = 960 minutes

∴ 280x = 70 × 960

(3) Find the third proportional of:

(4) Find the mean proportional between:

(5) (i) A : B = 3 : 5 = (3 × 4) : (5 × 4) = 12 : 20

B : C = 4 : 7 = (4 × 5) : (7 × 5) = 20 : 35

∴ A : B : C = 12 : 20 : 35

(ii) x : y = 2 : 3 = (2 × 5) : (3 × 5) = 10 : 15

y : z = 5 : 7 = (5 × 3) : (7 × 3) = 15 : 21

∴ x : y : z = 10 : 15 : 21

(iii) m : n = 4 : 9 = (4 × 1) : (9 × 1) = 4 : 9

n : s = 3 : 7 = (3 × 3) : (7 × 3) = 9 : 21

∴ m : s = 4 : 21

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