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