Question

We have 6 english books and 6 math books.. In how many ways we can arrange the books if only two english books are together and the rest are not together

Answer 1

@Kainui

Answer 2

Treat the two english books as if they are a single item to be arranged on the shelf. So you really have now instead of 12 different things, 11 different things. How many ways can you arrange 11 things on a shelf?

Now once you figure that out, just consider that every single one of those arrangements you had an item that could actually have been placed in two different ways, so multiply your answer by 2 to get both situations. Done!