Question

Sam needs to cut a piece of sheet metal into 8 pieces. It takes him 5 minutes to make each cut.

Answer 1

-- Cut the sheet in half. 

-- Put one half-sheet on top of the other half-sheet.
Cut the stack of 2 halves in half.

-- Put one stack of two quarter-sheets on top of the other stack of quarter-sheets.
Cut the stack of 4 quarters in half.

Now you have eight one-eighth sheets.

Three cuts.
Taking Sam (3 x 5) = 15 minutes, plus a few seconds for set-up between cuts.

Answer 2

For #3, To make 8 pieces you have 7 cuts. 7*5=35 minutes