The number of daily orders at a cloud kitchen rose by 25% in one month and then fell by some per cent in the next, finishing 5% above where it started. By what per cent did the orders fall in the second month?

Take the starting figure as 100. After the rise it is 125, and it must finish at 105. So $125\times (1-f)=105$, giving $1-f=105/125=0.84$ and $f=0.16$, a fall of 16%. 20% is the trap of subtracting the two figures (25 - 5), which forgets that the fall is taken on 125, not on 100. 30% adds them instead, and 25% assumes the fall must exactly undo the rise.