Posted by **Nicole** on Sunday, October 2, 2011 at 12:17am.

Susan has some $2-coins and $5-coins. If there are 18 coins and the total amount of these coins is not less than $75, find the minimum number of $5-coins.

- Math -
**hurrdurrbeedooda**, Sunday, October 2, 2011 at 12:54am
Let x = 2$ coins

Let y = 5$ coins

First equation is for the total amount of coins:

x + y = 18

Second Equation is for total amount in dollars in total from the coins:

2x + 5y = $75

Lets isolate for y

x = 18 - y

Sub into second equation

2(18 - y) + 5y = 75

36 - 2y + 5y = 75

3y = 39

y = 13

Therefore, you must have at least 13 $5 coins.

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