Another way to think about it: for every 100 units in 10, you take 67. That adds up to 6.7.
On a 67% off sale, an item originally priced at $10 would be discounted by $6.7, bringing the price to $3.3.
Whether you are calculating a discount, a tax, a tip, or a commission, the math is always the same: multiply 10 by 0.67.