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Maths Trick #2

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3 May 2012 14:58:53 IST
Posts: 12
3 May 2012 14:58:53 IST
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Maths Trick #2
Engineering Entrance , JEE Main , JEE Advanced , Mathematics , academic , Mathematical Logic
This is a simple quicker math trick but it can be very useful for young students to solve seemingly difficult calculations. I will be glad to get your feedback on this.

Mental multiplication by 5, 25, 50, 250, 500 and so on. Any number can be expressed in different ways. For example, 5 can be expressed as 10x(1/2).

Trick: Multiplication by 5

Step 1: Multiply the number by 10, i.e. simply place a zero after the number.

Step 2: Halve the resultant number.

Example 1:

5 × 136 = ten times of 136 i.e. 1360 should be divided by 2 = 1360/2 = 680

Example 2:

5 × 343, half of 3430 is 1715

Also check out, how to mentally multiply by 111?

Trick: Multiplication by 50, 500, 5000 and so on..

The above logic can also be applied to 50 which is half of 100 i.e. 1/2x100

Instead of multiplying the number by 10 we have to multiply by 100. So we have to place two zeroes after the number.

Example 1:

50 × 136 = hundred times of 136 i.e. 13600 should be divided by 2 = 13600/2 = 6800

Example 2:

50 × 647 = hundred times of 647 i.e. 64700 should be divided by 2 = 64700/2 = 32350

Same logic can be extended to numbers like 500, 5000 and so on.

Trick: Multiplication by 25

For multiplication by 25, we have to go one step further, 25=100 x (1/2) x (1/2)

Step 1: Multiply the number by 100, i.e. simply place two zeroes after the number.

Step 2: Halve the resultant number.

Step 3: Again halve the resultant number.

Example 1:

25 × 136 = hundred times of 136 i.e. 13600 should be divided by 2 = 13600/2 = 6800. Again halve this number, 6800/2 = 3400

Example 2:

25 × 343, half of 34300 is 17150. Again half of 17150 is 8575.

The above logic can also be extended to numbers like 250, 2500 and so on.
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