MULTIPLYING TWO DIGIT NUMBERS BY ONE DIGIT NUMBERS

We can follow the steps given below to multiply a two digit number by a one digit number mentally.

Step 1 :

Break the two digit number into tens and ones.

Example : The two-digit number 23 is close to the round figure 20. So, we can break 23 into (20 + 3). The two-digit number 29 is close to the round figure 30. So, We can break 29 into (30 - 1).

Step 2 :

Multiply tens by the one digit number.

Steps 3 :

Multiply ones by the one digit number.

Step 4 :

Add the results of step 3 and step 4.

Solved Examples

Evaluate each of the following expressions.

Example 1 :

14 x 5

Solution :

= 14 x 5

= (10 + 4) x 5

= 10 x 5 + 4 x 5

= 50 + 20

= 70

Example 2 :

12 x 9

Solution :

= 12 x 9

= (10 + 2) x 9

= 10 x 9 + 2 x 9

= 90 + 18

= 108

Example 3 :

24 x 6

Solution :

= 24 x 6

= (20 + 4) x 6

= 20 x 6 + 4 x 6

= 120 + 24

= 144

Example 4 :

19 x 6

Solution :

= 19 x 6

= (20 - 1) x 6

= 20 x 6 - 1 x 6

= 120 - 6

= 114

Example 5 :

38 x 5

Solution :

= 38 x 5

= (40 - 2) x 5

= 40 x 5 - 2 x 5

= 200 - 10

= 190

Example 6 :

49 x 7

Solution :

= 49 x 7

= (50 - 1) x 7

= 50 x 7 - 1 x 7

= 350 - 7

= 343

Example 7 :

78 x 4

Solution :

= 78 x 4

= (80 - 2) x 4

= 80 x 4 - 2 x 4

= 320 - 8

= 312

Example 8 :

81 x 6

Solution :

= 81 x 6

= (80 + 1) x 6

= 80 x 6 + 1 x 6

= 480 + 6

= 486

Example 9 :

93 x 7

Solution :

= 93 x 7

= (90 + 3) x 7

= 90 x 7 + 3 x 7

= 630 + 21

= 651

Example 10 :

99 x 9

Solution :

= 99 x 9

= (100 - 1) x 9

= 100 x 9 - 1 x 9

= 900 - 9

= 891

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