How do you figure out a percentage off of original price?

Basically to figure out the percentage of an original price you can either do the following:

1) Find out the percentage of the amount you want off then take it away:

For example if you wanted 40% of a £30 shirt, you would times the amount by 0.n (n is the percentage). Therefore £30 x £0.40 which is £12.

Afterwards you then deduct this from the original amount of £30. So 40% off a £30 shirt the sale price would be £18.

2) You could also take away first before multiplying:

100% - 40% = 60%

£30 x 0.6 = £18

NOTE: If you wanted 5% off then you would need to times by 0.05!