A store pays a 6% commission on the first $500 in sales and and 8% on sales over $500. Find the commission on an $800 sale

First you need to understand the structure of the commission.

The first part is 6% commission on sales up to $500.

The second part is 8% commission on sales over $500.

Note that the second part doesn't mean that a sale of $800 gets 8% of $800.

It means that once we have reached $500, any * further * sales get 8%.

Since $800 is $300 more than $500, the commission is

6% of $500 +

8% of $300

The first thing she did was work out the excess above $500.

Then she worked out the two percentages in two separate parts.

The second part seems to have incurred a cut and past accident, not sure if that is yours or it was already done.