Set up an proportion first. It looks like this:
Part Percent
————— = —————
Whole 100%
10 is your percent, 30 is your whole, 100 is always 100, and you don’t know the part so it is x (unknown).
It now looks like this:
X 10
————— = —————
30% 100%
Step by step explanation:
1) multiply across
30 • 10 = 300
2) divide what’s left over
300 / 100 = 3
So 10% of 30 is 3.