SAT Math Practice Exam

Answer A The average of x and y = (x+y)/2
If you add the two given equations, you find
3x + 5y = 10
5x + 3y = 30
__________
8x +8y = 40
or x+y = 5
Hence average = 2.5

Key takeaway: One way may be to go for solving the two linear equations and find the variables. But that may be a longer rout. So always first look for any other way to attack such problems. Sometimes simply adding or subtracting the two equations may yield the desired result.