The multiplication method we saw last week was to find the product of two-digit numbers with the same first digit and second digits having a sum of 10. So the second digits were 1 and 9, 2 and 8 etc. Today we look at the same multiplication but where the digits whose sum needs to be 10 are 5 and 5.

Example: 25 x 25

The tens digit for both is 2. The sum of the units digits is 5 + 5 = 10. So we use the same method as earlier.

Multiply the tens digit by the next consecutive number. That will be the first part of our answer. 2 x 3 = 6

Multiply the units digits of the two numbers. That will be the second part of the answer. 5 x 5 = 25

Answer: 625

Multiplication of such two-digit numbers is actually squaring the number.

Consider 35 x 35. The tens digit of the both numbers is 3 and the sum of the units digits is 10.

1. Multiply 3 (the tens digit) by the next number, 4. 3 x 4 = 12. This is the first part of the answer.

2. The product of the units digits is the second part of the answer. 5 x 5 = 25.

Answer: 1225

Let us see some more examples.

65 x 65

1. Multiply 6 (the tens digit) by the next number, 7. 6 x 7 = 42. This is the first part of the answer.

2. The product of the units digits is the second part of the answer. 5 x 5 = 25.

Answer: 4225

We can apply this method to find the square of any number ending in 5. Say we have to find the square of 125, 12 can be used for getting the first part of the answer and 5 to get the second part of the answer.

195 x 195

1. Multiply 19 by the next number, 20. 19 x 20 = 380. This is the first part of the answer.

2. The product of the units digits is the second part of the answer. 5 x 5 = 25.

Answer: 38025

Now you can try these:

1) 45 x 45

2) 75 x 75

3) 125x125

4) 205 x 205