Question

the sum of the ages of 3 person is 150 years . 10 years ago their ages were in the ratio 7:8:9. their present ages are

Answer 1

ten years ago, their ages were in the ratio 7:8:9, so you can assume their ages 10 years ago to be 7x, 8x and 9x respectively. 
as of now, their ages would be 7x + 10, 8x + 10 and 9x + 10 
the sum of these ages is 150, so: 
7x + 10 + 8x + 10 + 9x + 10 = 150 
or, 24x + 30 = 150 
or, 24x = 150 - 30 = 120 
or, x = 120/24 = 5 
so their present ages are 7*5 + 10, 8*5 + 10 and 9*5 + 10 
i.e. 45, 50 and 55