Answer :

It is easier (for me anyway) to find 10% then work around that.
Following that path would mean that, by making a table:

100% = 220
10% = 22
5% (Which is half the 10) = 11

What number is 5% of 220?

Since we don't know what number it is, we can use X.

The word "of" means multiply, so we can rewrite the problem.

X = 5% × 220

X = .05 × 220

X = 11