Twelve students took a group photo, with 4 people in the front row and 8 people in the back row. Now the photographer needs to select 2 people from the 8 people in the back row and move them to the fr

Twelve students took a group photo, with 4 people in the front row and 8 people in the back row. Now the photographer needs to select 2 people from the 8 people in the back row and move them to the front row. The relative order of the others remains unchanged.

840

Solution: Choose 2 people from the 8 people in the back row***.

These 2 people are inserted into the 4 people in the front row and guaranteed The order of the people in the front row remains unchanged.

First, insert one person from the 5 gaps among the 4 people. There are 5 insertion methods;

The remaining person must insert into the 5 slots in the front row. There are 6 interpolation methods for human neutral position. ∴ is

then the number of different adjustment methods is = 840.