Multiplying Two Numbers with the same Tens Digit and whose
Ones Digits add up to 10
There is a neat little trick for multiplying two numbers with
the same tens digit where the ones digits add up to 10. An
example of this type of problem is 23 Ã— 27. The tens digit is
the same, 2, and the ones digits add up to 10, 3 + 7 = 10. Use
the following steps.
 Multiply the ones digits together. Write the product on
the right and use two digits of the answer.
 Multiply the tens digit times 1 plus the tens digit.
Write the product to the left.
Example:
23 Ã— 27 =
 Multiply 3 Ã— 7 = 21. Write 21 to the right.
 Multiply 2 Ã— (2 + 1) = 2 Ã— 3 = 6. Write 6 to the left.
621.
23 Ã— 27 = 621.
Example:
49 Ã— 41 =
 Multiply 9 Ã— 1 = 9. Remember to use two digits. Since 9
is only one digit in length, write 09 to the right for
the answer.
 Multiply 4 Ã— (4 + 1) = 4 Ã— 5 = 20. Write 20. 2009.
49 Ã— 41 = 2009.
Advanced Trick
This trick also works when their are more than 2 digits in the
numbers. For example, to multiply 134 Ã— 136, you conside the
“tens digit” to be 13.
Example:
134 Ã— 136 =
 Multiply 4 Ã— 6 = 24. Write 24 to the right.
 Multiply 13 Ã— (13 + 1) = 13 Ã— 14 = 182. Write 182 to
the left. 18224.
134 Ã— 136 = 18224.
