find how many coins there are in a sock drawer.

Question

There are 28 coins in a sock drawer. Each coin is either a dime or quarter. The total value of the coins is $4.00. Write two equations to model this situation, and solve the system to find how many quarters and how many dimes there are. 

Answer 1

D + Q = 28 --> Q = 28 - D

 

10D + 25Q = 400 pennies

 

10D + 25( 28 - D) = 400

 

10D + 700 - 25D = 400

 

700 - 400 - 15D = 0

 

300 = 15D

 

D = 300/15 = 20

 

Q = 28 - D = 28 - 20 = 8

 

25 * 8 + 20 * 10 = 200 + 200 = 400 pennies = $4.00

 

There are 8 quarters and 20 dimes