Quick Pricing Calculations

Mental Math · Axiom Academy

Nudge the price, then use the trick that fits the count Shift the price to the nearest friendly quarter, multiply that by whichever route this unit gave you for the quantity — halve-and-take-ten for five, ten-groups-less-one for nine, a quarter of a hundred for twenty-four — and then hand the pennies back. The nudge and the give-back cancel exactly, so what comes out is the real total, not an estimate. Never divide in the aisle — multiply across Which pack is cheaper per unit? Dividing hands you two ugly decimals. Multiply across instead: the price of A times the size of B, against the price of B times the size of A. The smaller product is the cheaper pack, and that is a proof , not an estimate. Round the prices first if you like — but only trust the rounded answer when the two products land further apart than the rounding could possibly have moved them. A discount is a multiplication with a friendly factor Ten percent is a decimal point moved one place — and nearly every other sign in the window is built out of that one move. Twenty is the ten doubled, thirty is the ten tripled, five is half the ten, fifteen is the ten plus its own half. Twenty-five and fifty do not even need the ten: halve, and halve again. Round every line — then know which way you are wrong

This is the written version of the interactive lesson above. See the full Mental Math course.