Math Shortcut - a% of b = b% of a

a% of b = b% of a

• It’s not immediately clear, but it’s true: a% of b = .01 * a * b, which is the same as b% of a (.01 * b * a).
• What’s 16% of 25? The same as 25% of 16: 4
• What’s 43% of 200? Same as 200% of 43: 86.

Source: Mental Math Shortcuts