It’s fun to sell our stuff we don’t need, buy stuff we don’t need, and eat nacho fries and drink lemonade at the Friday night auction! But the auction house gets their cut, so how much do we really make? The auction house charges 20% on anything we sell, and upcharges 10% on anything we buy. Let’s say we sell a bunny cage for $100, and buy a bicycle for $30. How much do we take home?
First, we take $100*20% and subtract that from the $100 the buyer paid.
That leaves us with $100-$20=$80.
A shortcut would be to take $100*.8=$80.
To purchase the bicycle, we bid $30. Then we must add 10% of this.
$30*10%+$30=$33
A shortcut would be to take $30*1.1=$33
So in the end, we brought in $80, and spent $33 leaving $80-$33=$47 in our pockets!
Be sure to invite your teens into the work of choosing and fixing up what you will sell, and allow them to spend some of the proceeds. This will draw them into the story problem, especially when they hear, “Yup! Yup!” on items they are selling. And they must quickly figure out how much they have to spend, so they can make that next, “Yup!” Discuss the math with them quickly, and pull out your phone calculators to play the what-if game. This is problem solving at its finest!