Question

Find the fourth proportional to the following:

`1/7, 1/5, 1(1)/7`

Answer 1

Let x be the fourth proportional

`1(1)/7 = 8/7`

⇒ `(1/7)/(1/5) = (8/7)/x`

⇒ `1/7 xx 5 = 8/(7x)`

⇒ `5/7 = 8/(7x)`

⇒ 5 × 7x = 7 × 8

⇒ 35x = 56

⇒ x = `56/35`

⇒ x = `8/5`

⇒ x = `1(3)/5`

The fourth proportional is `1(3)/5`.