Squaring Numbers Ending in 5

Squaring Numbers Ending in 5
Presented by Grey Matters Mental Gym
http://members.cox.net/beagenius/

Squaring a number is simply multiplying it by itself. For example, 8 squared (8 2 ) is simply 8 * 8, or 64. Conversely, the square root of 64 would be 8.
Squaring numbers ending in 5 are particularly easy. It’s also useful in extracting the square root of any number.

Have a spectator give you any number from 1 to 100 that ends in 5.
Imagine being able to figure the square of that number in your head!

Squaring Numbers Ending in 5 Requirements
Calculator
Spectator

To be able to square numbers ending in 5 mentally, you must know your times tables up to 10 times 10.

When you’re given a two-digit number ending in 5, focus on the digit in the tens place.
For example, let’s say you’re given the number 35. In this case, you would focus on the 3.

Simply multiply the tens digit by a number 1 higher than itself.
Since we’re focusing on the “3” in 35, we would multiply 3 time 4 (1 higher than 3) to get 12.

To finish, simply add “25” to the end of the number you just calculated. That’s the answer!
Taking 35, we focused on the “3”, multiplying 3 times 4 to get 12. Adding “25” to the end gives 1,225, which is the answer to 35 squared (35 2 ).

Other examples:
What is 75 2 ? 7 times 8 is 56, so the answer is 5,625.

Other examples:

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Squaring Numbers Ending in 5

by greymatters on Jan 18, 2007

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