Ten copies plus one
How to multiply by 11 mentally
Eleven is 10 + 1. Instead of recalling a special rule, make one copy ten times larger and add the original number. This works for every number and stays easy to verify.
The pattern
n × 11 = (n × 10) + n
Step by step
- 1Multiply the number by 10.
- 2Keep one unchanged copy of the original number.
- 3Add both values.
Worked examples
23 × 11
230 + 23
253
47 × 11
470 + 47
517
125 × 11
1,250 + 125
1,375
For two-digit numbers you may know the shortcut of adding the middle digits. The 10 + 1 method is slightly longer, but it handles carries and larger numbers without changing the rule.
Try the pattern
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