Each small piece is 6 inches because 72 / 12 = 6. Each piece is then 5 inches long after the knots are tied because 6 - 1 = 5. The three pieces tied together are now 15 inches long because 5 x 3 = 15.
This justifies what answer for what question? Q & A:
Vincent has 72 inches of rope that he wants to use for a project, but he needs to cut it into smaller pieces first. He cuts it into 12 equal length pieces, but then he realizes it's too short, so he ties three pieces together. The knots then make each piece 1 inch shorter. How long are his pieces of rope after all this?
15