In 10 years, A will be twice as old as B was 10 years ago. If A is now 9 years older than B, the present age of B is :  Choose the correct choice from the following answers.
A) 19  B) 29  C) 39  D) 49  E) None of these
Explanation:   Let B's present age = x years. Then, A's present age = (x + 9) years.   (x + 9) + 10 = 2(x - 10)   =&gt; x + 19 = 2x - 20   =&gt; x =39. Answer: 39
<result>C</result>
In 10 years, A will be twice as old as B was 10 years ago. If A is now 9 years older than B, the present age of B is :