Special Multiplication methods
To find the product of two-digit numbers whose tens digit is the same and the sum of whose units digits is 10.
Example: 23 x 27
The tens digits of the two numbers is the same (2) and the sum of the units digits (3+7) is 10.
Multiply the tens digit with its next number. 2 x 3 = 6
Multiply the units digits. 3 x 7 = 21
Combine the two to get the answer: 621
Example: 81 x 89
Multiply the tens digit with its next number. 8 x 8 = 72
Multiply the units digits. 9 x 1 = 09
Combine the two to get the answer: 7209
When we multiply numbers ending with 1 and 9 we need to write the product of the units digits as a tw0-digit number. So we write it as 09.
Now we can try doing the problems in a single step.
42 x 48 = (4 x 5) / (2 x 8) = 20 16
74 x 76 = (7x 8) / (4 x 6) = 56 24
To find the product of two-digit numbers where the sum of the tens digits is ten and the units digit is the same.
Example: 23 x 83
The units digits of the two numbers is the same (3) and the sum of the tens digits (2+8) is 10.
Multiply the tens digits and add the units digit. 2 x 8 + 3 = 19
Multiply the units digits. 3 x 3 = 09 (Remember that we need a two-digit answer)
Combine the two to get the answer: 1909
Example: 96 x 16
Multiply the tens digits and add the units digit. 9 x 1 + 6 = 15
Multiply the units digits. 6 x 6 = 36
Combine the two to get the answer: 1536
In a single step:
34 x 74 = (3 x 7) +4 / 4 x 4 = 25 16
49 x 69 = (4 x 6) + 9 / 9 x 9 = 33 81
Now you can try:
43 x 47
51 x 59
46 x 66
85 x 25
Tip of the week: Interest helps us to explore new methods