1.Why do you multiply to change from a larger unit to a smaller unit?

2. A carpenter cuts 2 ft 9 in. off a board that has 4 ft long. How long is the piece that is left , in feet and inches?

1 answer

larger unit = foot
smaller unit = inch -- more inches than feet in the same length

2.
4 - 2 ft, 9 in = 3 ft. 12 in - 2 ft, 9 in = ?