# Need help

#### zekit

##### New Member
hey guys, I found this forum using google. and I really hope you guys can help me.
This is the question:

Every box of a smartphone has a coupon with a number inside. the number can be: 1,2,3,4,5. If someone get all the coupons with all the numbers, he win a free phone.

the first question is: "what is the probability of a person who bought 5 phones, NOT to win a free phone". and the answer is:0.9616. - this part wasn't the problem.

The following question, is the one I cannot solve:
"What is the probability of a person who bought 8 phones, to win a free phone"

the problem I have is that now he is buying 8 phones, and I'm not sure what I need to do...

Any help would be greatly appreciated.

#### Prometheus

##### Member
If you worked out the probability of no win with 5 phones, you should be able to work out the probability of no win with 8 phones easily.
Once you know that you can make use of the idea that the sum of all probabilities equals 1 to work out the probability of winning with 8 phones.

#### zekit

##### New Member
in order to answer the first question I found out what is the probability to win, than did 1-probability .

I've been siting on this for about 6 hours now, still no idea what to do