Another way to think about it: for every 100 units in 10, you take 90. That adds up to 9.
90% of 10 equals 9. This applies to discounts, tips, taxes, interest rates, or any scenario where you need 90 out of every 100 parts of 10.
Whether you are calculating a discount, a tax, a tip, or a commission, the math is always the same: multiply 10 by 0.9.