Another way to think about it: for every 100 units in 10, you take 33. That adds up to 3.3.
On a 33% off sale, an item originally priced at $10 would be discounted by $3.3, bringing the price to $6.7.
Whether you are calculating a discount, a tax, a tip, or a commission, the math is always the same: multiply 10 by 0.33.