+1405 I have $3$ different mathematics textbooks, $2$ different psychology textbooks, and $2$ different chemistry textbooks. In how many ways can I place the $7$ textbooks on a bookshelf, in a row?
+1139
I have $3$ different mathematics textbooks, $2$ different psychology textbooks, and $2$ different chemistry textbooks. In how many ways can I place the $7$ textbooks on a bookshelf, in a row?
7 • 6 • 5 • 4 • 3 • 2 • 1 = 5040 ways
You can make 7 choices for the first book.
That leaves you 6 choices for the next book.
And then there are 5 choices for the third book.
and so on
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