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 be25. 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 is225.

**b) What is 25² ?**

We know the last two digits of the square will be25. 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 is625.

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

Practice Problems

1. 115²

2. 205²