Mrs. conley asks her class what kind of party they want to have to celebrate their excellent behavior. out of all the students in the class, 5 want an ice cream party, 7 want a movie party, 10 want a costume party, and the rest are undecided. if 20%, percent want an ice cream party, how many students are in the class?

Let's write an expression for the number of students in the class:

5+7+10+x

Of this total number of students, 5 want an ice cream party.  This constitutes 20% of the class, or the decimal fraction 0.20.

Thus,           5
              = 0.2 or 1/5
               5+7+10+x

 Then           5           1
                =
                 22+x         5

Solving for x:  25 = 22 + x; x=3

Then the total number of students in the class is 22+x = 22+3 + 25.

Check:  is              5
                              equal to 0.20?  YES
                              25