Sunday, October 6, 2013

Finger multiplication

The use of finger multiplication has been widespread through the years. It is not the traditional way of doing multiplication in school today.

However, if your kid has trouble remembering the whole multiplication table, multiplication with fingers is a good alternative

To multiply with fingers, you are only required to remember the multiplication table up to 5 × 5.

After that, all multiplication can be performed with your fingers

Here is the technique:

The two numbers to be multiplied are each represented on a different hand

Each hand may have some raised fingers and some closed fingers at the same time

Number of fingers to raise = Factor − 5. Remember that a factor is a number in a multiplication problem

The sum of the raised fingers is the number of tens

The product of the closed fingers is the number of ones

Example #1:

7 × 8

For 7, use your left hand and raise 2 fingers (Factor − 5 = 7 − 5 = 2) . This means there are 3 closed fingers

For 8, use your right hand and raise 3 fingers. This means that there are 2 closed fingers

Sum of raised fingers = 2 + 3 = 5. This means we have 5 tens or 50

Product of closed fingers = 3 × 2 = 6. This means that we have 6 ones

50 + 6 = 56

Example #2:

9 × 6

For 9, use your right hand and raise 4 fingers. This means there is 1 closed finger

For 6, use your left hand and raise 1 finger. This means that there are 4 closed fingers

Sum of raised fingers = 4 + 1 = 5. This means we have 5 tens or 50

Product of closed fingers = 1 × 4 = 4. This means that we have 4 ones

50 + 4 = 54

Example #3:

8 × 5

For 8, use your left hand and raise 3 fingers. This means there are 2 closed fingers

For 5, use your left hand and raise no finger. This means that there are 5 closed fingers

Sum of raised fingers = 3 + 0 = 3. This means we have 3 tens or 30

Product of closed fingers = 2 × 5 = 10. This means that we have 10 ones or 1 ten or 10

30 + 10 = 40

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