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### How to Find the Square of Number ending with 5?

We know

• 5² = 25
• 15² = 225
• 25² = 625

Now see the similarity. In all these numbers the last two digits are same. That is 25. The only thing it changes is the first digit.

How to find that?

a) What is 15² ?
We know the last two digits of the square will be 25. Now take the first digit of 15; i.e. 1. Multiply 1 with it’s next number. i.e. 2. So 1 x 2 = 2. Answer is 225.

b) What is 25² ?
We know the last two digits of the square will be 25. Now take the first digit of 25; i.e. 2. Multiply 2 with it’s next number. i.e. 3. So 2 x 3 = 6. Answer is 625.

c) What is 55² ?
(5 x 6) 25 = 3025

d) What is 85² ?
(8 x 9) 25 = 7225. Hardly it takes less than 5 seconds. You don’t even need to write the numbers on the paper.

Try 105²
As usual (10 x 11) 25 = 11025 is the answer. Our usual method will take a minimum of 30 seconds to do this simple multiplication. Now we can easily
save 25 seconds.

Practice Problems
1. 115²
2. 205²