# Binomial probability

• Nov 11th 2009, 10:19 PM
Vicky1997
Binomial probability
A poll shows that 70% of all voters approve of the mayor's work. On three separate occasions a pollster selects a voter at random. What is the probabilty that on exactly one of these three occasions the voter approves of the mayor's work?

Could someone please explain this as easy as possible?(Happy)

Vicky.

Thanks.
• Nov 12th 2009, 03:05 AM
mr fantastic
Quote:

Originally Posted by Vicky1997
A poll shows that 70% of all voters approve of the mayor's work. On three separate occasions a pollster selects a voter at random. What is the probabilty that on exactly one of these three occasions the voter approves of the mayor's work?

Could someone please explain this as easy as possible?(Happy)

Vicky.

Thanks.

If X is the random variable 'number of voters who approve of the mayor' then X ~ Binomial(n = 3, p = 0.7). Calculate Pr(X = 1).
• Nov 12th 2009, 07:34 PM
Vicky1997
Quote:

Originally Posted by mr fantastic
If X is the random variable 'number of voters who approve of the mayor' then X ~ Binomial(n = 3, p = 0.7). Calculate Pr(X = 1).

Thanks for your help. But I don't know what Binomial probability means.
But I could think of three cases

1st person 2nd person 3rd person

1 approve disapprove disapprove

2 disapprove approve disapprove

3 diapprove disapprove approve

Vicky.

• Nov 12th 2009, 10:27 PM
mr fantastic
Quote:

Originally Posted by Vicky1997
Thanks for your help. But I don't know what Binomial probability means.
But I could think of three cases

1st person 2nd person 3rd person

1 approve disapprove disapprove

2 disapprove approve disapprove

3 diapprove disapprove approve

Vicky.

Calculate the probability of each outcome. Add the results. That's the answer.
• Nov 14th 2009, 09:14 PM
Vicky1997
Quote:

Originally Posted by mr fantastic
Calculate the probability of each outcome. Add the results. That's the answer.

I think I got the answer.

7/10 X 3/10 X 3/10 = 63/1000

3/10 X 7/10 X 3/10 = 63/1000

3/10 X 3/10 X 7/10 = 63/1000

189/1000

Thanks!!!
• Nov 15th 2009, 02:28 AM
mr fantastic
Quote:

Originally Posted by Vicky1997
I think I got the answer.

7/10 X 3/10 X 3/10 = 63/1000

3/10 X 7/10 X 3/10 = 63/1000

3/10 X 3/10 X 7/10 = 63/1000

189/1000

Thanks!!!

Correct. (And you're welcome).