gajala wrote:
why not 9c3= 84 ways
I also used to struggle with when to just write out ___ X ___ X ___ and when to use the formula. In this case, consider what the formula means "9 choose 3" But we are not really choosing 3. We are choosing 1 per room, or better said, we are choosing any of them for a room and then any of the left ones and then a final time. Perhaps someone else can give an example of this same question reworded so that the formula would be needed? Perhaps if we had 9 fossils, one display room and this one room was going to display 3 fossils at the same time?