Cross Multiplication Method

Mental Math · Axiom Academy

LESSON Cross Multiplication Method Two two-digit numbers in one pass: the leading pair gives the hundreds, the crossing pairs give the tens, the trailing pair gives the ones — and the carry ripples left. 1. Three Places, and the X in the Middle Write the two numbers one above the other and there are exactly four ways to pair a digit from the top with a digit from the bottom. Two of those pairings run straight down ; two of them cross . Take 23 × 12 . Straight down on the left: 2 × 1 = 2 , and that is the hundreds. The two crossings: 2 × 2 = 4 and 3 × 1 = 3 , and both of them land in the tens, so the tens column holds 4 + 3 = 7 . Straight down on the right: 3 × 2 = 6 , the ones. Read the columns left to right — 2, then 7, then 6 — and the answer is 276 . Leading pair. Multiply the two leading digits. That is the hundreds column. Crossing pairs. Multiply each leading digit by the other number's trailing digit, then add those two results. That sum is the tens column. Trailing pair. Multiply the two trailing digits. That is the ones column. Then read the columns left to right. Three columns — and the middle one is a sum of two products Three more with nothing to carry While every column stays at 9 or below, the column totals are the answer digits and there is nothing else to do. 2. A Column Holds One Digit — the Rest Moves Left

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