Question

Find the third proportional to the following:

3, 12

Answer 1

Let x be the third proportional to 3, 12.

Third proportional to 3, 12 is the same thing as fourth proportional to 3, 12, 12, then

3 : 12 :: 12 : x

⇒ `3/12 = 12/x`

⇒ 3 × x = 12 × 12

⇒ 3x = 144

⇒ x = `144/3`

⇒ x = 48