Squaring a number ending in 5 | Answer to mental math challenge and the mathematical explanation
A couple of days ago I have posted a mental math challenge of squaring the number 65 without a calculator.
• Squaring a number ends with 5 | mental #ma...
This video provides the mathematical explanation (proof) of the trick.
1. The squared number always ends in 25.
2. The digits before 25 is just the digit before the 5 in the original number, multiply by the next integer of that digit.
So for example, to find 65^2, write down 25, then take the digit before 5 (in this case, 6) and find the next integer (in this case 7) and find the product of these two digits (which is 42). So the answer is 4225.
To find 75^2, take the next integer after 7, which is 8 and multiply it with 7. This gives us 56 and the square of 75 is 5625.
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