19 boys and 13 girls
Rewrite the word problem as an equation:
Use elimination. Subtract the top equation from the bottom equation:
Now plug into one of the equations. I will plug into the first one:
It is possible to answer the question without using any equations or algebra at all.
The number of student is
However, with the number of girls doubled, the total is
Therefore the difference in the two totals is the number of girls, because the number of girls was added on again.