in 10 year, A willbe twice as old as B was 10 year ago. if A is now 9 year older then B, the present age of B is
Choose one:
A) 19 years
B) 29 years
C) 39 years
D) 49 years
E) None of these
Solution   Let B's present age = x years. then, A's present age = ( x + 9 ) years.   ∴ (x + 9) + 10 = 2 (x - 10) ⇔ x + 19 = 2 x - 20 ⇔ x = 39. Answer 39 years
<result>C</result>
in 10 year, A willbe twice as old as B was 10 year ago. if A is now 9 year older then B, the present age of B is