Question

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?

Answer 1

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.