A man puts a dollar under his bed on day 1, 2 dollars the next day, 3 dollars on day 3, and so on. After 15 days, he takes the stash and buys $100 worth of food. How much is left in the stash?
He should, after 15 days, have: [15 x 16] / 2 =$120.00
$120 - $100 = $20.00 left
