Peter bought 45 greeting cards at 3 for $2.00. he sold them for 5 for $4.00. how much money did he make

Step 1) Set up a proportion to find how much Peter spent

45 cards / x dollars = 3 cards / 2 dollars

Step 2) Cross-multiply to solve the proportion

3x = 90

x = $30

Step 3) Set up a proportion to find how much Peter made

45 cards / x dollars = 5 cards / 4 dollars

5x = 180

x = $36

Step 4) Subtract the amount Peter made by the amount he spent

36 - 30 = $6

Peter made $6

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