A learner counting up from -12 in steps of 4 reports that 4 steps are needed to reach 0. How many steps are actually needed?

الشرح

The count runs -12, -8, -4 and 0, which is four values joined by three moves, so three steps of four carry it from twelve below zero up to zero. Counting the values instead of the moves between them overstates the number of steps by exactly one, whatever the length of the list.