SOLUTION: Evan is 6 years old. His sister is 15 years old. How old will they both be when Evan is half as old as his sister?

Let x = how many years to get the condition under the question.


Then at that time, Evan will be 6+x years old; His sister will be 15+x years old.


The condition is

    2*(6+x) = 15+x.


Simplify and solve

    12 + 2x = 15 + x

    2x - x = 15 - 12

     x     = 3.


The problem is just solved.


It will happen in 3 years.


Evan will be 6+3 = 9 years old;  his suster will be  15+3 = 18 years old.   ANSWER