A total of 315

tickets were sold for the school play. They were either adult tickets or student tickets. The number of student tickets sold was two times the number of adult tickets sold. How many adult tickets were sold?

Let x be the number of tickets sold to adults and y the number sold to students:

x + y = 315. But we know that y was double x, then:

y = 2x

Plug the value of y (in the 1st equation) by 2x:

x + 2x = 315

3x = 315

and x = 105 (which is the number of tickets sold to adults