A 20 foot piece of rope will be cut into as many 3 and 1\2 foot section as possible. how much rope will be left over?

20/(3 1/2) = 20/(7/2) = 20*2/7 = 40/7 = 5 5/7

so, 5 pieces, plus 5/7 of a piece left over.

Since one piece is 7/2 feet, 5/7 * 7/2 = 5/2 = 2 1/2 feet left over.

Or, 20 - 5(3 1/2) = 20 - 17 1/2 = 2 1/2 ft left over