Wednesday, 30 July 2008

Inflation Method In Mental Maths

There are many methods to do mental math division. One method is presented here.
I call it the Inflation method.

The key concept is to multiply the number (denominator) to a "better" or simpler number to operate.

What is these "better" number ?
Examples of "better" number are 10, 20 , or 100 .

Let us do an example to see the process.

34 / 5 = ?

5 when multiplied by 2 gives 10 which is a "better" number.

Therefore to maintain the original math question, we need to multiply the numerator by 2 also.

(34 x 2) / (5 x 2) = 68 / 10 ==> 6.8 ANSWER.

For the Divide by 5 question:
Alternatively, we can short-cut the above step by multiplying the numerator by 2 and later shifting the decimal point of the answer one digit to the left.

NOTE:
- Choosing the multiplication of numerator by 2 is because of the "5" division number,
- Shifting the decimal point to one digit to the left is similar to dividing by 10.
- Denominator is not multiplied by 2 because the decimal point shifting cater for that step.

Example of Decimal Shifting method:
34 / 5==> Numerator: 34 x 2 = 68.0==> Shift decimal point to left: 6.80 (Final answer).

Another example of using Inflation method for Mental division: 26 / 25

Steps:
1) Denominator 25 x 4 = 100 ( a "better" number)
2) Numerator also x 4 ==> 26 x 4 = 104

Answer : 104 / 100 = 1.04 All done mentally!

Visit the Deflation Method in Mental Division for another alternative to solving the maths problem.

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1 comment:

Irene Sng said...

Interesting method to do mental division. The twin technique of inflation and deflation give us a choice. Great work and thinking!
At least these 2 methods can release us of the need for calculator at times.