How to Multiply by 12 in Your Head
Multiply by 10, then add double the original.
34 × 12 = 408
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Twelve 34s is ten of them plus two of them.
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The two of them is a double: 34 × 2 = 68.
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Add the parts: 340 + 68 = 408.
How do you multiply by 12 in your head?
To multiply by 12, multiply by 10 and add double the original number. For 34 × 12, take 34 × 10 = 340, add 34 × 2 = 68, and get 340 + 68 = 408.
It works because twelve of something is ten of them plus two more, so splitting 12 into 10 + 2 turns one hard step into two easy ones.
A two-digit number with a large units digit works the same way: 47 × 12 = 470 + 94 = 564. So does a bigger number: 125 × 12 = 1250 + 250 = 1500. When the number is a multiple of 25, another split is faster, because 12 is also 4 × 3: 75 × 12 = 75 × 4 × 3 = 300 × 3 = 900. Check the last digit before trusting an answer: 47 × 12 must end in 4, because 7 × 2 = 14.
Your turn
Three to try in your head. Tap what you get.
29 × 12 = ?
96 × 12 = ?
73 × 12 = ?
All 36 shortcuts: the Magic Tricks library.