Question

What number must be added to each of the numbers 15, 17, 34 and 38 to make them proportional?

Answer 1

Let x be added to each number, then numbers will be
15 + x, 17 + x, 34 + x, and 38 + x.
Now according to the condition
`(15 + x)/(17 + x) = (34 + x)/(38 + x)`
⇒ (15 – x)(38 + x) = (34 + x)(17 + x)
⇒ 570 + 53x + x² = 578 + 51x + x²
⇒ x² + 53x – x² – 51x = 578 - 570
⇒ 2x = 8
⇒ x = 4
∴ 4 is to be added.