Word Problem - Great fun :)

[cnmath]

There are 7 textbooks in total; the question asks to rearrange the 3 mathematics textbooks so that they are all together.

This is my answer:

The math textbook can be arranged as 3! ways

Then, arrange all of the books in 5! ways (math together as one and 4 other books) -- how does this idea look?

 

[Denis]

HINT:
mmm1234, mmm1243, ...., mmm4321
1mmm234, 1mmm243, ...., 4mmm321
.....
1234mmm, 1243mmm, ...., 4321mmm