Deduct (percentage) amounts off of specific quantity ranges

Hello all,


I'm interested in learning how to deduct a percentage off of a range of units.

For example, if I have 100 units that cost $50, I'd like to deduct 20% off of the first 10 units, and then have the total dollar amount put into a separate cell.

So, 100 x $50 = $5000

With 20% off of the first 10 units: $4900.

__________________________

20% of $50 = $10

$10 x 10 units = $100

$5000 - $100 = $4900