Caculating Percentages Mentally

Knowing how to calculate percentages mentally is not only important for kids to know, but also for adults.  How many times do we face a situation where we go to a store to buy some clothes and find out that there is a discount of a certain percentage?  If we can calculate the new value right away, we'd be able to figure out how much extra money would be left after the discount and see if we want to buy some other items with that difference.

There is a very quick way to calculate any percentage in few seconds.  All you have to do is break the percentage into two more familiar percentages (i.e. 5%, 10%, 50%, 100%).  Those percentages are more familiar, because they are very simple to calculate.  For instance, to obtain 10% of any value, we just move the decimal place once to the left, and 5% is half of that value.  To get 50% of a number, we divide by 2.

I will give couple examples to make matters clearer,

40% of 200 = ?

40% = 50% - 10%

50% of 200 = 200/2 = 100

10% of 200 = 20.0

Hence, 40% of 200 = 100 - 20 = 80

98% of 260 = ?

98% = 100% - 2% (and 2% = 10% / 5)

100% of 260 = 260

2% of 260 = 26.0/5 = 5.2

So, 98% of 260 = 260 - 5.2 = 254.8

This technique demonstrates that percentages are very easy to calculate, so long as we keep things simple.