You have a log that is 20 feet long, and you are breaking it into 2-foot long sections. We are cutting it into 10 equal pieces, each piece is 2 feet long (20 feet ÷ 2 feet = 10 pieces) I am going to make a diagram where an equal sign, =, is a piece of the tree, and a slash, /, is a cut.
If we look at this, there are 10 pieces, and 9 cuts. "Bob can cut through a log in two minutes." This means that each of the 9 cuts takes 2 minutes, 9×2=18 It will take Bob 18 minutes to cut up the log
