Oh, wow! A real life math problem (instead of the made-up stinkers in the text--if I can't count the number of coins in my collection, I'm sure not going to use algebra to try to figure how many dimes, nickels, and quarters are in it!): What is the minimum you can write your check for to make sure $15 goes to the fundraiser, while still paying 5% of the total in a fee to PayPal? 15 + 5% of N = 100% of N.
Change those pesky percents into decimals, and we get 15 + .05N = 1N.
After collecting like terms, we have 15 = 1N - .05N, which simplifies to 15 = .95N.
Isolate the variable, and we get N = 15/.95, so N = $15.79, assuming, of course, that PayPal doesn't have minimum increments.
Thank you, guys. I love showing my students math in real life, so I'll take this one to class with me next week.
(BTW, send $16 if you are using PayPal, not $15.75
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