Mental Math Worksheets
Solutions for
Multiplying Two - Digit numbers Mentally Using patterns
What is the pattern for those type of multiplications?
1) Same tens digit (labeled by red),
2) The sum of the ones digit is 10 (labeled by green),
How to multiply those numbers mentally just in one second?
There are two parts in the answer, for instance, 23 × 27
First part (labeled by red): Tens digit × (Tens digit + 1), 2 × (2 + 1) = 2 × 3 = 6,
Second part (labeled by green): Multiply the ones digits, 3× 7 = 21, if their product less than 10, write 0
First: 1 × 9 = 09. The answer just write these two parts together, so 23 × 27 = 621,
The 1stpart in Answer
The 2nd part in Answer
11 × 19 =
1 × (1 + 1) = 1 × 2 = 2
1 × 9 = 09
209
23 × 27 =
2 × (2 + 1) = 2 × 3 = 6
3 × 7 = 21
621
46 × 44 =
4 × (4 + 1) = 4 × 5 = 20
6 × 4 = 24
2024
72 × 78 =
7 × 8 = 56
2 × 8 = 16
5616
53 × 57 =
5 × 6 = 30
3 × 7 = 21
3021
69 × 61 =
6 × 7 = 42
1 × 9 = 09
4209
35 × 35 =
3 × 4 = 12
5 × 5 = 25
1225
84 × 86 =
8 × 9 = 72
4 × 6 = 24
7224
99 × 91 =
9 × 10 = 90
9 × 1 = 09
9009
68 × 62 =
6 × 7 = 42
8 × 2 = 16
4216
*108 × 102 =
10 × 11 = 110
8 × 2 = 16
11016
*
15 × 16 = 240
7 × 3 = 21
24021
Question
157 × 153 =
Answer
*This method can be extended to three digit numbers with identical first two digits and with the sum of
ones digits equals to 10.
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