The number to be added to each of the numbers 7, 16, 43, 79 to make the numbers in proportion is = ?

Answer: Option C

7, 16 , 43, 79
If a, b, c, d are in proportion
⇒ a : b :: c : d
Then ad = bc
Let x is added to make it a proportion
⇒ (7 + x) : (16 + x) :: (43 + x) : (79 + x)
⇒ (7 + x)(79 + x) = (16 + x)(43 + x)
∴ x² + 86x + 553 = x² + 59x + 688
⇒ 27x = 135
⇒ x = 5
∴ Hence, it 5 is added to make it a proportion