Question

In 10 years A will twice as old as B was 10 years ago if A is now 9 year older than B the find present age of B ?

Answer 1

Let B's age = x years. 
Then, As age = (x+ 9) years. 
(x+9+10)=2(x—10) 
hence x=39. 
Present age of B = 39 years

Hope This Helps :)

Answer 2

Let age of A be x and B be y.
CaseI.
10+x=2y-10
Case2.
x=9+y
Substituting x value in case 1.
10+9+y=2y-10
19+y=2y-10
y=29.
substituting y value in case2.
x=9+y
x=8+29
x=38.
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