Check Multiplication with 9s Trick

Problem

Verifying multiplication results requires recalculating the entire problem.

Solution

Use casting out nines: Sum digits of each number repeatedly until single digit, then verify.

Benefit

Quick verification method that catches 90% of calculation errors.

Example

Verify: 234 × 56 = 13,104

234: 2+3+4=9 → 9
56: 5+6=11 → 1+1=2
9 × 2 = 18 → 1+8=9

13,104: 1+3+1+0+4=9 ✓
Answer is likely correct!