Squaring any two digit number ending in five
In this lesson, we will show you how straightforward squaring any two digit number ending in five can be
First look at the following multiplication
Did you make the following important observation?
The answer always ends in 25. This will be the case when you square any two digit number ending with 5
Now, how did we get the number(s) before 25? Easy!
Look for the number in the tens place.For the multiplications above, these are 2, 4, and 1
Multiply each number by its next higher digit
So,
2 × 3 = 6
4 × 5 = 20
1 × 2 = 2
Put these numbers on the left of 25
Other examples
1) 35 × 35
The digit in the tens place is 3
Multiply 3 by its next higher digit, which is 4
3 × 4 = 12
Write down 12 and put 25 next to it
The answer is 1225
2) 55 × 55
The digit in the tens place is 5
Multiply 5 by its next higher digit, which is 6
5 × 6 = 30
Write down 30 and put 25 next to it
The answer is 3025
3) 95 × 95
The digit in the tens place is 9
Multiply 9 by its next higher digit, which is 10
9 × 10 = 90
Write down 90 and put 25 next to it
The answer is 9025
Important note:
Before you can really apply these tricks, you must know your multiplication table by heart
Have you learned your
muliplication table yet?
If having problems to learn the multiplication table by heart, have you tried
finger muliplication ?