Question

The average age of three boys is 25 years and their ages are in the proportion 3 : 5 : 7. The age of the youngest boy is

Answer 1

Answer:

age of youngest boy is 15 years

let a,b, c be the ages of 3 boys

given proportion can be written as

a:b = 3:5 & b:c = 5:7

from above proportions we can write

a= (3b/5) & c=(7b/5)

also it is given that

25=(a+b+c)/3. -(1)

substitute value of a & c in above eqn (1)

(3b/5) + b + (7b/5) = 75

solving above LCM we get

(10b + 5b)/5 = 75

15b = 375

b = 25

but a= ( 3b/5) = (3*25/5) = 15

therefore age of youngest boy is 15 years