Thread: [SOLVED] Binomial Probability

Hi,

I am having trouble with the following question:

During winter it rains on average 18 out of 30 days. Five winter days are selected at random. Find (4 d.p) the probability that:

(a) the first two days chosen will be fine and the remainder wet
My approach is this is an ordered selection:

I have defined p = it will rain = or 0.6
q = 1 - 0.6 = 0.4
=
= 0.03456

The answers I have are yielding 0.0124.

(b) more rainy days than fine days have been chosen
P(3 rainy days) =
P(4 rainy days) =
P(5 rainy days) =
= 0.3456 + 0.2592 + 0.007776
= 0.612576

The answers are yielding 0.7102

I wonder where I am going wrong
TIA for any assistance!

Originally Posted by lindah

Hi,

I am having trouble with the following question:

During winter it rains on average 18 out of 30 days. Five winter days are selected at random. Find (4 d.p) the probability that:

(a) the first two days chosen will be fine and the remainder wet
My approach is this is an ordered selection:

I have defined p = it will rain = or 0.6
q = 1 - 0.6 = 0.4
=
= 0.03456 .... Looks right to me

The answers I have are yielding 0.0124.

(b) more rainy days than fine days have been chosen
P(3 rainy days) =
P(4 rainy days) =
P(5 rainy days) =
= 0.3456 + 0.2592 + 0.007776 ..... 0.07776
= 0.612576 ...... 0.68256

The answers are yielding 0.7102

I wonder where I am going wrong
TIA for any assistance!

See above

Sorry for the miscalc!!!
Then it looks like the solutions may be incorrect on this one.

I have been tearing my brain apart on it
Thank you!!