# Permutation and combination

1. ### kschong

5
For this question, i already solve the part a and part b. For the part c, i try to solve it but i cant get the answer that given. Can someone explain to me? How to do the part c. Thanks!

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2. ### tiny-tim

26,054
Hi kschong!

So there's 24 tanks, of which 6 are high viscosity, add 4 are high impurity: what is the probability that 4 tanks chosen at random include exactly one of each?

Show us your full calculations, and then we can see what went wrong, and we'll know how to help.