How many codes with five letters can be made from the letters of D R A G O N F L Y if the first and last letters have to be vowels and each letter can only be used at most once?     *210 *840 *240 *420 *None...

I think the answer is 308 but I'm not sure.

A table is set with 13 large numbered (and thus distinguishable) bins. We have 5 red balls (indistinguishable ones) and 8 blue balls (also indistinguishable). We are interested in the...

I used the following method and got the right answer: What I did was removed 4 of the 12 stations leaving 8 stations and 9 gaps,  then I selected 4 out of 9 gaps giving me 9C4 please explain...

c) Allowing for unlimited repeats, what is the probability if we selected a 7 letter arrangement at random that it would contain no repeated letters? d) How many 7 letter arrangements...

Permutations     in how many ways can five examinations be scheduled in a week so that no two examinations are scheduled on same day considering sunday as a holiday

a rectangular table has 4 seats on one side and 3 seats on the opposite side.   a family of 7 consist of 2 grandparents, 2 parents and 3 children are to be seated at the table. In how...