# Math

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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 -

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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