the knowledge hub
Byte-sized articles to sharpen your mind
Short pieces that teach one thing properly, for students and for the parents and teachers reading over their shoulder.
Shortcuts and tricks to solve problems faster.
- 2 min readsample
Multiply any two digit number by eleven, in your head
Split the digits, add them, and drop the sum in the middle. It works because multiplying by eleven is the same as multiplying by ten and adding the number again.
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Squaring any number that ends in five
Take the digits before the five, multiply by the next number up, and stick 25 on the end. Twenty five squared is 6 followed by 25, because two times three is six.
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