HOW TO CALCULATE PERCENTAGE IN YOUR HEAD WITHOUT PEN ON PAPER

PERCENTAGES

This week, we will be considering how to calculate percentages.

While you can use a calculator to figure out percentages, there is a simple method you can use to solve them in your head. The best part is you probably are familiar with the basic skills for calculating percentages, which are calculating 10% and 50%.

Calculating 10%. Calculating 10 percent of a number is the same as dividing the number by 10. The procedure to divide a number by 10 is to move the decimal point one spot to the left. For example, to calculate 10% of 123 is the same as dividing the number by 10. This is accomplished by moving the decimal point over 1 spot to the left, which means that 12.3 is 10% of 123. Similarly, 10% of 56 is 5.6 and 10% of 4987.56 is 498.756.

Calculating 50%. calculating 50 percent of a number is the same as dividing the number by 2, which means to half the number. For example, to calculate 50% of 123 is the same as halving 123. So, 50% of 123 is 61.5. similarly, 50% of 56 is 28 and 50% of 5000 is 2500.

Calculating other percentages. You can calculate most percentages in your head if you can calculate 10% and 50%! The reason is that many percentages can be found as a combination of 10% and 50%.

Let’s do an example of calculating 15% of 63. Note that 15% is equal to 10% plus 5%. To do this, you can calculate 10% and then half of 10% (which is 5%) to half itself. So, we can calculate 10% of 63 is equal to 6.3. then we calculate 5% as half of that, which is 3.15. so, we add these together to get 9.45. which is 15% of 63.

Let’s do another example of 25% of 84. Note that 25% is equal to half of 50%. So, we can calculate 25% of 84 by finding 50% and then halving the result. We can readily calculate that 50% of 84 is equal to 42, and then we need to take half of that number to get 21. Therefore, we have 25% of 84 is equal to 21.

Here is some short guide.

5% = half of 10%

10% = divide by 10

15% = add 10% and half of 10%

20% = find 10% and then double it

25% = find 50% and then half it

30% = find 10% and then triple it

40% = find 10% and 50%. Subtract 10% value from 50% value

50% = divide in half

60% = find 10% and 50%. Add 10% value to 50% value

75% = find 50% and 25% and add together

80% = find 20% (double 10%) and subtract from the whole.

90% = find 10% and subtract from the whole.

Note that there can be more than one way to calculate a given percentage. For example, you can also calculate 60% by finding 10% and then multiplying that value by 6. You can do the same thing for 20, 30, 40, 60, 70, 80, and 90.

Exercise

Click here to see some simple questions