Read the problem, pick which shortcut applies — train the recognition reflex
Spot the Method — name the shortcut before you solve.
A problem flashes up, e.g. 47 × 5. Instead of computing it, you pick which mental-math shortcut applies from four buttons. ×5 is “×10 then halve”; a subtrahend ending in 9 is “equal addition”; a divisor of 12 is “halve, halve, ÷3”. Some problems have no shortcut — and spotting that is part of the skill. Problems interleave across +, −, ×, ÷ so you discriminate the cue, not just the operation.