Another way to think about it: for every 100 units in 10, you take 65. That adds up to 6.5.
On a 65% off sale, an item originally priced at $10 would be discounted by $6.5, bringing the price to $3.5.
Whether you are calculating a discount, a tax, a tip, or a commission, the math is always the same: multiply 10 by 0.65.