In my college days, we used a similar trick question to harass (or ragging as known in India) juniors. Beginning with $100 how much will you be left with if you lose 50% and gain 50%?
This is a technique often used in gambling games (poker apps minigames etc.)
They offer a series of actions that let you lose or gain x% n many times in a row, with an equal chance of each. The fact that +x% doesn't cancel out a -x% compounds on the difference in lay person expectations to produce horrific odds for microtransactions.
