# Math Help - HELP! Probability of odds in favor of obtaining

1. ## HELP! Probability of odds in favor of obtaining

Compute the odds in favor of obtaining?

At least 1 head when a single coin is tossed 3 times?

help me please i know the answer is 7:1 but how and what did they do to get that answer?

2. ## Re: HELP! Probability of odds in favor of obtaining

It is certain that for three tosses that there is either no heads (event X) or at least 1 head (event Y). Thus:

$P(X)+P(Y)=1$

$P(Y)=1-P(X)$

Now, what it the probability of no heads (3 tails)?

3. ## Re: HELP! Probability of odds in favor of obtaining

so how do they get the ratio 7:1?

5. ## Re: HELP! Probability of odds in favor of obtaining

okay well thats the whole questions im not really familiar with this so i really dont know what other information i need to get to you.

6. ## Re: HELP! Probability of odds in favor of obtaining

What I mean is, I am asking you to compute the probability that all three tosses are tails. Once you do this, then you can complete the question.

What is the probability that for 1 toss, the result is tails?

1/2

8. ## Re: HELP! Probability of odds in favor of obtaining

Correct, so for three tosses in a row to all be tails, what would this probability be?

3/2 ?

10. ## Re: HELP! Probability of odds in favor of obtaining

No, the probability of getting the first tail AND getting the second tail AND getting the third tails is:

(1/2)(1/2)(1/2) = 1/8

You see, there are 8 outcomes, only one of which is 3 tails:

HHH
HHT
HTH
HTT
THH
THT
TTH
TTT

11. ## Re: HELP! Probability of odds in favor of obtaining

okay i see that now. so how do i go about finding the ratio ?

nvm i got it

13. ## Re: HELP! Probability of odds in favor of obtaining

Yes, you can see now, even without the formula that there are 7 outcomes with at least 1 heads and only 1 without. The formula is useful though...for example if instead of 3 tosses there are 100 and listing the 2^100 outcomes is just not practical.