Another way to think about it: for every 100 units in 10, you take 75. That adds up to 7.5.
On a 75% off sale, an item originally priced at $10 would be discounted by $7.5, bringing the price to $2.5.
Whether you are calculating a discount, a tax, a tip, or a commission, the math is always the same: multiply 10 by 0.75.