Atotal of 679 tickets were sold for the school play. they were either adult tickets or student tickets. there were 71 fewer student tickets sold than adult tickets. how many adult tickets were sold?

For example a stands for the number of adult tickets, and s stands for the number of student tickets.

Write a system of equation based on the problem
An equation for "A total of 679 tickets were sold for the school play"
∴ a + s = 679 (first equation)
An equation for "there were 71 fewer student tickets sold than adult tickets"
∴ s = a - 71 (second equation)

Find the solution of the system
Subtitute s with a - 71 in the first equation to find the value of a
a + s = 679
a + a - 71 = 679
2a - 71 = 679
2a = 679 + 71
2a = 750
  a = 750/2
  a = 375
The number of adult tickets sold is 375