Tips For Success

Some questions on tests ask you to solve a problem that involves a system of equations. Read the sample question below.

Then follow the tips to answer the question.

TIP 1 When writing an equation, try to use variables that make sense for the problem. Instead of using x and y, use q for quarters and n for nickels. Melissa keeps a jar for holding change. The jar holds 21 coins. All of the coins are quarters and nickels. The total amount in the jar is $3.85. How many quarters are in the jar?

TIP 2 Make sure to answer the question asked. Here you only need to find the number of quarters.

1. 3
2. 7
3. 14
4. 21

Think It Through

Write a system of equations.

q + n = 21 q plus n equals 21

0.25 q + 0.05 n = 3 . 85 0.25 , q plus , 0.05 , n equals 3 . . 85

Solve the first equation for n and substitute to find q.

0.25 q + 0.05 n = 3.85 0.25 q + 0.05 ( 21 − q ) = 3.85 0.2 q + 1.05 = 3.85 q = 14 table with 4 rows and 2 columns , row1 column 1 , 0.25 , q plus , 0.05 , n , column 2 equals , 3.85 , row2 column 1 , 0.25 , q plus , 0.05 , open 21 minus q close , column 2 equals , 3.85 , row3 column 1 , 0.2 q plus , 1.05 , column 2 equals , 3.85 , row4 column 1 , q , column 2 equals 14 , end table

The correct answer is C.