# Math Help - Probability

1. ## Probability

Hi all =)

Question...
A fair coin is tossed thrice. Supposed we denote a "head" turning up as 1 and
"tail" as 0. Given that the total on all three tosses is an odd number,
what is the probability that at first toss, we get a "head"?

i dont have any idea to start answering this question..

2. Originally Posted by nameck
Question...
A fair coin is tossed thrice. Supposed we denote a "head" turning up as 1 and
"tail" as 0. Given that the total on all three tosses is an odd number,
what is the probability that at first toss, we get a "head"?
Here is your outcome set. You count them
$\begin{array}{ccc}
1 & 1 & 1 \\
1 & 1 & 0 \\
1 & 0 & 1 \\
1 & 0 & 0 \\
0 & 1 & 1 \\
0 & 1 & 0 \\
0 & 0 & 1 \\
0 & 0 & 0 \\

\end{array}$

3. Originally Posted by Plato
Here is your outcome set. You count them
$\begin{array}{ccc}
1 & 1 & 1 \\
1 & 1 & 0 \\
1 & 0 & 1 \\
1 & 0 & 0 \\
0 & 1 & 1 \\
0 & 1 & 0 \\
0 & 0 & 1 \\
0 & 0 & 0 \\

\end{array}$
should i use conditional probability?

4. Originally Posted by nameck
should i use conditional probability?
How many odd sums?

5. Originally Posted by Plato
four..

6. Originally Posted by nameck
four..

7. There are four odd sums and there are four start with a one.

8. Originally Posted by nameck
There are four odd sums and there are four start with a one.
That is wrong. Count again.
$\begin{array}{ccc}
1 & 1 & 1 \\
1 & 0 & 0 \\
0 & 1 & 0 \\
0 & 0 & 1 \\

\end{array}$

9. 1 1 1
1 1 0
1 0 1
1 0 0

0 1 1
0 1 0
0 0 1
0 0 0