# Help on Extension Probability (1 Viewer)

#### bmn

##### Member
Just acouple of questions:

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.

#### Drongoski

##### Well-Known Member
Q1(b): did you get 128/3125 ?? Your expression looks right to me (Binomial Prob)

Last edited:

#### bmn

##### Member
Q1(b): did you get 128/3125 ?? Your expression looks right to me (Binomial Prob)
Yes I'm getting that...

2/10 x 11/20

#### bmn

##### Member
2/10 x 11/20
Working backwards from the answer I could find that. But how did you get 11/20?

#### azureus88

##### Member
if its between 300 and 500, its gotta be 3 digits so you can only pick from 10 to 20 (which is 11/20)

#### bos1234

##### Member
you can only pick numbenrs 3,4 from the first deck

and in the second deck you can only pic numbres from 10-20 (inclusive)

say you pick 3 next deck you pick 18 combingin the numbers =318

so, 2/10 x 11/20