Quick Square
A mathematical trick
Did you know that there is a quick way of squaring a two digit number which ends in 5?
Just multiply the first digit by that number plus one.... stick a 25 after your product and there's your answer .... simple ?
Example:
Q. What is 35 squared?
A. 3x4=12
.....now stick on the 25
...........the answer is 1225
Barry's Response - It even seems to work with three digit numbers (using the first two digit to make a two digit number) and plain old 5, using 0 as the first digit.
Oh the handy things we can do with
math, games,
conversions and tricks.
Search this site for more information now.
Here are some other math shortcuts and tricks:
You can use these shortcuts for
mental math and quick calculations.
- A two-digit number can be multiplied by 11 by adding the two digits and putting the sum in the middle. 11 x 24 is 264, for example.
- You can multiply a number by 9 by multiplying it by 10 and subtracting the original number. The answer to 9 x 7 is 70 - 7, which equals 63.
- If you wanna multiply by 5, divide a number by 2 and then add a 0 to the end. For example, 5 x 36 is 36 ÷ 2 = 18, then add a 0 to get 180.
- If you want to square a two-digit number, find the nearest multiple of 10, then calculate the difference between the number and the multiple, square this difference, and add it to the multiple squared. To find 37 squared, find the nearest multiple of 10, which is 40. Calculate 37 - 40 = -3, square -3 to get 9, and add that to 40 squared, which is 1600. Therefore, 37 squared is 1600 + 9 = 1609.
- To multiply by 25, multiply it by 100 (by adding two zeros) and then divide it by 4. To find 25 x 48, calculate 48 x 100 = 4800, then divide it by 4, which equals 1200.
- To multiply a number by 50, multiply it by 100 (by adding two zeros) and then divide the result by 2.
- A number is divisible by 3 if the sum of its digits are divisible by 3. Check with 246.
Calculate 2 + 4 + 6 = 12, which is divisible by 3, so yeah, divisible by 3.
- Same check can be used for divisible by 9.