To find 10% of any number, move the decimal point one spot to the left.
so, 10% of 100.0= 10.00
10% of 78.0 = 7.8
10% of 5618.0= 561.8
And once you know 10%, you can find 5% (by halving your 10%) and you can find 20% (by doubling), 30% (by doubling and adding 10% on again) 40% (by doubling and doubling again) and 50% should be easy (you just halve the original number) etc.
Remember to just move the decimal point one spot to the left.
There endeth todays lesson