1) the probability that advertisements are showing when changing TV channels at rnadom is 2/5. If george changes channels 6 times during an even find the probability that advertisements are showing:

a) on 2 occasions (Done that)

b) More the 4 times

I'm doing 6C5*(2/5)^5*(3/5) + 6C6*(2/5)^6. Where am I going wrong? Not getting the answer in the book.

2) A card is chosen at random from a set of 10 cards numbered 1 to 10. A second card is chosen from a set of 20 cards numbered 1 to 20. Find the probability that the combination number these cards make is:

c) between 300 and 500

I know the first card has a 2/10 chance, but I don't know what I'm meant to times it with.