SAT Mathematics Practice Test 4

Since the average of 2 numbers is the sum of the 2 numbers divided by 2, the equations x=

m+9

9

,y=

2m+15

2

and z=

3m+18

2

are true. The average of x, y, and z is given by

x+y+z

3

Substituting the preceding expressions in m for each variable gives

m+9 2 + 2m+15 2 + 3m+18 2

3

This fraction can be simplified to

6m+42

6

or m+7 Choices A, C, and D are incorrect and may be the result of conceptual errors or calculation errors. For example, choice D is the sum of x, y, and z, not the average.