Seven piles of bricks are placed side by side so that their tops form steps 1 brick high. If the lowest pile contains 9 bricks, how many bricks are being used altogether?
If the lowest pile contains 9 bricks, the next pile contains ten bricks, the next contains eleven, and so on until the greatest contains 15 bricks. The sum is thus 9+10+11+12+13+14+15=84.
