The calculation process is not required to be 300 yuan. Buy 10 get one free, then buy 1000 get one free 100. There are just 1 100 students in the school, so it is 1000× 3 = 3000 yuan. And it costs 3300 yuan to buy one by one.

If you need a process:

It is known that I bought 1 1 30 yuan.

1 100 ÷ 1 1 = 100,

100×30 yuan = 3000 yuan.

1 100× 3 = 3300 yuan

3,300 yuan-3,000 yuan = 300 yuan