+842 I have $4$ different mathematics textbooks and $3$ different psychology textbooks. In how many ways can I place the $7$ textbooks on a bookshelf, in a row, if all the psychology textbooks are together?
+42 First, let's assume the psychology textbooks are one bundle. Then, there are obviously 5!=120 ways to organize the four textbooks and the bundle. Next, there are 3!=6 ways to arrange the different psychology books inside the bundle. Therefore, there are 120*6= \(720\) ways to organize the textbooks.
Feel free to tell me if I made a mistake! :D
