How do you figure out percents in your head?

Question

I know that whatever % I have i just move the decimal and times it so like 10 % of 20
so
.10*20=2
But how do you do that in your head....i cant multiply decimals in my head very fast...is their an easy way to look at percents?

Answer 1

I just divide the number by 100 then multiply by the percent I want. What 27% of 150? 1% = 1.5, 1.5 x 27=40.5

Answer 2

I think you've got it.

The thing to realize, is that the percent doesn't move the decimal, % is the symbol for /100, so 10% really is 10/100 or one tenth 1/10 = 0.1. Finding (1/10) of a number is easy, you just move the decimal to the left one place: one tenth of 3 is .3, of 30 is 3, of 3.5 is .35 of .0005 is .00005. That's 10% of all these numbers.

Once you have 10% you can find 20%, 30%, 40% etc by multipling what you found 10% to be by 2, 3, or 4.

E.g. 20%(3) = 2(.3) or .6

To add 5% that's half of 10% or 10%/2.

So 15%(20) = (10%)20 + (1/2)10%(20)

= 2 + 2/2 = 3

Combine this with the above fellow's suggestion for finding 1% of a quantity and there you have it. 17%

= 10% + 10%/2 + 2(1%)

17%(20) = 2 + 1 + 2(.2) = 3.4

Answer 3

Reduce everything to combinations of 1, 5 and 10 percent.

10 percent - move the decimal once.
5 percent - half of 10 percent.
1 percent - move the decimal twice.

So if you need to figure out 22 percent of 57, say, it's this:

20 percent of 57 plus 2 percent of 57

1 percent of 57 is .57 x 2 = 1.14

20 percent of 57 is 2 X 10 percent (5.7, doubled is 11.4)

so 1.14 + 11.4 = 12.54.

The way to learn how to do this fast is to do it over and over, practice on things you don't need to practice on. Then it will become second nature.

Answer 4

It seems to come easily to some people and not to others. All I do in figuring out a tip, for example, is to mentally "move the decimal" to find 10 percent, then I mentally take half of that and add to the original to find 15 percent, etc.

Answer 5

Just shift the decimal afterwards. In our example:
10 * 20 = 200
Now shift the decimal two places to the left -> 2.00 = 2.

One more example: 15% of 50?
15*50 = 15*5 and a zero added = 750
Decimal two places to the left -> 7.50 = 7.5

Regards
HMM

Answer 6

10/20
=1/2
=1/2*100
=50%
first you find 10/20 as a fraction ie 1/2, then multiply it by 100 in your head.. This gives the desired percentage..

Answer 7

Here's how I do it.

Divide 100 by the percent.

100/10 = 10.

Divide the number of which youre taking the percent by this dividend.

20/10 = 2.