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,

*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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Question The 1stpart in Answer

The 2nd part in Answer

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 *157 × 153 =

15 × 16 = 240 7 × 3 = 21 24021