In Part 1, we taught you how to multiply two-digit numbers where the units digit is same and the sum of the numbers at tens digit is 10?

Now, let’s interchange them.

Method 3:

How do we find the product of two-digit numbers where tens digit is the same and the sum of the units digits is 10?
For example,
34 x 36
Note the sum of the units digits (4+6) is 10 and the tens digits of the two numbers is the same, i.e, 3

Step 1:
Multiply the tens digit with its next number.
3 x 4 = 12

Step 2:
Multiply the units digits
4 x 6 = 24

Step 3:
Combine the answers obtained in step 1 and 2 to get the correct answer:
1224 (34 x 36 = 1224)
Simple! Isn’t it?

Method 4: Multiplication by factors

Example 1: 44 x 14

Since we know 14 = 2 x 7, multiplication by 14 can be easily achieved. Hence, in order to multiply any number by 14, we will first multiply it by 2 and then multiply the answer by 7.

Step 1:
44 x 14 = 44 x (2 x 7)

Step 2:
First multiply 44 by 2, i.e,
44 x 2 = 88

Step 3:
Multiply the number obtained in step 2 with 7 to get the answer, i.e.,
88 x 7 = 616
Answer: 44 x 14 = 616

Example 2:

Step 1:
79 x 81 = 79 x (9 x 9)

Step 2:
Multiply 79 by 9, i.e,
79 x 9 = 711

Step 3:
Multiply the number obtained in step 2 with 9 to get the answer, i.e.,
711 x 9 = 6399
Answer: 79 x 81 = 6399

Method 5: When the multiplication involves 25 or 50

Example: 44 x 25

We know that 25 is one-quarter of 100, that is, 100 /4 = 25. So instead of multiplying by 25, we will multiply the number by 100 and then divide the answer by 4.

Step 1:
44 x 25 = 44 x 100/4

Step 2:
Multiply the number by 100
44 x 100 = 4400

Step 3:
Divide the answer obtained in Step 2 with 4
4400/4 = 1100
The number obtained is the required answer, i.e, 44 x 25 = 1100
Similarly, when multiplying with 50, the fraction will become 100/2. The rest of the method will remain the same.