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 | 1,702 |
2 | 2,412 |
3 | 2,202 |
4 | 3,852 |
5 | 1,809 |
| 11,977 |
The next month (after spending some money on an ad) they sold 3 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?