Three times as old as my sister was -Math Riddle


One sister says of her younger sister: 
"Two years ago, I was three times as old as my sister was. In three years's time, I will be twice as old as my sister.? How old are they each now?

 

Explanation :  

One way to solve this math  is to use even numbers: The elder sister will be twice as old as her younger sister in three year's  time. This immediately rules out the elder sister currently being 8, 11, and 14, so she must be 17, and the younger sister 7.