A math test has 25 problems. Some problems are worth 2 points and some are worth 3 points and the total for the test is 66. How many 2 points and 3 points promblems are there.

x-->2pt questions
y-->3pt questions

1)  x+y=25  <--- total questions
2)  2x+3y=66 <--- total points

Using substitution:
2x+3(25-x)=66
2x+75-3x=66
75-66=x
x=9 
y=25-9=16 
there are 9 - 2pt problems and 16 - 3pt problems