Not sure how to test each statement in this Jane age question. How can I tell if one alone is sufficient?

Question

How old is Jane?
 1. Ten years ago she was one-third as old as she is now.
 2. In 15 years, she will be twice as old as she is now.

V Ritik · Accepted Answer

This is one of those DS questions where each statement actually gives you a clear equation.
Statement 1: If Jane is J years old now, then 10 years ago she was J &ndash; 10. The statement says she was one-third as old then as she is now. So: J &ndash; 10 = (1/3) * J That&rsquo;s just a simple equation you can solve. So yeah, statement 1 is enough by itself.
Statement 2: 15 years from now, Jane will be J + 15. The statement says that&rsquo;ll be twice her current age, so: J + 15 = 2 * J Again, clean equation, one variable, solvable. So this one&rsquo;s also enough on its own.
Both work individually. Answer is D.

Mansih K · Answer

You can test both statements one at a time by turning them into equations.
Statement 1: Ten years ago = J &ndash; 10 She was one-third of her current age &rarr; (1/3) * J So the equation is: J &ndash; 10 = (1/3) * J You can solve that, so statement 1 is sufficient.
Statement 2: In 15 years &rarr; J + 15 She&rsquo;ll be twice as old as now &rarr; 2 * J So equation: J + 15 = 2 * J Also solvable. One variable, one equation. Statement 2 is also sufficient.
So each on its own is enough. That&rsquo;s a D.