There are 30 coins inside a jar. Some of the coins are dimes and the rest are quarters. The total value of the coins is $3.20. How do you write a system of equations for this situation?

1 Answer
Jul 12, 2018
  1. quantity equation: #" "d + q = 30#

  2. value equation: #" "0.10d + .25q = 3.20#

Explanation:

Given: #30# coins in a jar. Some are dimes, some are quarters. Total value #= $3.20#.

Define variables:

Let #d# = number of dimes; #q# = number of quarters

In these types of problems there are always two equations:

  1. quantity equation: #" "d + q = 30#

  2. value equation: #" "0.10d + .25q = 3.20#

If you prefer working in pennies (no decimals), your second equation becomes:

#10d + 25q = 320#

Use substitution or elimination to solve.