Zack only has dimes and nickels in his car. He has 21 coins that value $1.50. How many dimes and how many nickels does he have in his car.

Question

Substitution 

Answer 1

Let x = the number of dimes and y = the number of nickels

 

We know that x + y = 21

 

We also know that the value of the coins is:

 

.10x + .05y = 1.50

 

10x + 5y = 150 (we obtain this result by multiplying both sides of the equation by 100 to clear decimals)

 

To use the Substitution Method, we can solve the first equation for y.

 

y = 21 - x

 

Now, for every value of y in the second equation, replace (or substitute) it with (21 - x)

 

10x + 5(21 - x) = 150

 

You should now be able to solve this linear equation for x, Desiree