basic probability question

[Rushinankil]

Could someone just tell me to about solving this question:

A saleswoman normally visits 60 homes in a week. She has a 20% chance of making a sale (indepent events)

If the woman was to only visit 12 homes, what is the probability of her making more than 6 sales?

Cheers,

[jay_shark]

This is a binomial distribution with p=20% , q=80% .

p=success
q=failure

Let x be a random variable of making a sale .

P(x=7) = 12c7(0.2)^7*(0.8)^5 There are 12 choose 7 ways of making 7 successful sales from 12 homes selected .

Similarly
P(x=8) =12c8(0.2)^8(0.8)^4

Continue in this manner by adding P(x=7)+P(x=8)+P(x=9) +P(x=10) +P(x=11) + P(x=12) which is equivalent to P(x>6)

The formula is P(X=x) = nCx*P^x*q^(n-x) , n=12 in this case

[Rushinankil]

Cheers,

I was always taught that the formula for binomial distribution was;

P(X=x) = (nCi)x(p^i)x(1-p)^n-i

Think I like your more condensed 1 tho.. cheers

[BruceZ]

[ QUOTE ]
This is a binomial distribution with p=20% , q=80% .

p=success
q=failure

Let x be a random variable of making a sale .

P(x=7) = 12c7(0.2)^7*(0.8)^5 There are 12 choose 7 ways of making 7 successful sales from 12 homes selected .

Similarly
P(x=8) =12c8(0.2)^8(0.8)^4

Continue in this manner by adding P(x=7)+P(x=8)+P(x=9) +P(x=10) +P(x=11) + P(x=12) which is equivalent to P(x>6)

The formula is P(X=x) = nCx*P^x*q^(n-x) , n=12 in this case

[/ QUOTE ]

This is 1 minus the probability of 6 or less, and in Excel you can use the function =BINOMDIST to do this sum for you as:

=1-BINOMDIST(6,12,0.2,true) =~ 0.39%

[Rushinankil]

cheers for that as well, i'll be needing that next semester.. in a few weeks time.lista