Sari sold 300 boxes of greeting cards in november. in december she sold 500. what was the percentage increase in her sales

There was a 66 % increase from Sari's sales from November to December. 

To find the percentage increase in her sales, we must first find the amount her sales increased. We can do that by subtracting the greeting cards sold in November from the number of greeting cards sold in December. Substituting values and simplifying, we get that she sold 200 more greeting cards in December.

To find what percent increase this is, we must find what percent 200 is of the number of greeting cards sold in November. We can do this by dividing 200 by the number of cards sold in November (300), and then multiplying by 100 (to make it a percent). Doing this, we get  * 100 which gives us our answer of 66 %.