A new fast food restaurant opened 5 months ago. The table belows shows the number of burgers they've sold so far.
Month | Burgers Sold |
1 | 1,898 |
2 | 3,868 |
3 | 1,720 |
4 | 2,513 |
5 | 3,049 |
| 13,048 |
The next month (after spending some money on an ad) they sold 9 times as many as they had sold in the previous 5 months. How many fewer burgers did they sell before running the ad than they did after running it?