Question

Four years ago the average of son's and father's age was 27.5. today the ratio of their age is 5: 16 find out the son's present age.

Answer 1

4years ago
(S + F)/2 = 27.5 years [given]
Hence sum of their ages 4 years ago
S + F = 55 years

sum of their present ages =
S + 4 + F + 4 = 55 + 4 + 4 [ age of both is increased by 4years]
hence adding 8 on both the sides we get
S + F = 63 years [sum of their present ages]

Now, ratio of S:F is 5:16
Using ratio and proportion
Son's age S is
(5 × 63)/(5+16) = (5 × 63)/ 21
i.e., 5 × 3 = 15 years

therefore, present age of son is 15years