# A few probability problems...

• Apr 7th 2009, 08:46 PM
bigtymer0011
A few probability problems...
I'm stumped on these questions I have no idea how to figure them out. Any help at all would be greatly appreciated. :)

1. A mountain search and rescue team receives an average of .83 calls per day. Find the probability that on a randomly selected day, they will receive more than two calls.

2. For a type of fabric, the average number of defects in each square foot is .78. Find the probability that a randomly selected square foot of fabric will contain more than 1 defect.

3. A sample of 4 different calculators are randomly selected from a group containing 13 that are defective and 30 with no defects. What is the probability that at least one of the calculators is defective?

Thanks for the help!
• Apr 7th 2009, 08:58 PM
skyslimit
For number 3 I believe you have a 4/13 probability that one is defective. Since the question asks only of defective calculators, you can ignore the effective calculators.

Hope someone can confirm this, for 1 and 2 not sure
• Apr 7th 2009, 09:01 PM
bigtymer0011
Quote:

Originally Posted by skyslimit
For number 3 I believe you have a 4/13 probability that one is defective. Since the question asks only of defective calculators, you can ignore the effective calculators.

Hope someone can confirm this, for 1 and 2 not sure

yeah but there are 43 total and you are selecting 4 randomly with 13 of the 43 being defective.
• Apr 7th 2009, 10:10 PM
mr fantastic
Quote:

Originally Posted by bigtymer0011
I'm stumped on these questions I have no idea how to figure them out. Any help at all would be greatly appreciated. :)

1. A mountain search and rescue team receives an average of .83 calls per day. Find the probability that on a randomly selected day, they will receive more than two calls.

2. For a type of fabric, the average number of defects in each square foot is .78. Find the probability that a randomly selected square foot of fabric will contain more than 1 defect.

3. A sample of 4 different calculators are randomly selected from a group containing 13 that are defective and 30 with no defects. What is the probability that at least one of the calculators is defective?

Thanks for the help!

1. The number of calls can probably be assumed to be modelled using a Poisson distribution.

2. The number of defects can probably be assumed to be modelled using a Poisson distribution.

3. 1 - Pr(none) $= 1 - \frac{^{30}C_4}{^{43}C_4}$.
• Apr 8th 2009, 06:16 AM
a69356
Hello everyone,

what is the difference between the Binomial distribution and Poisson distribution and Under which scenarios we can use Binomial distribution and Poisson distribution?

Any

Thanks,
Ashish
• Apr 8th 2009, 03:13 PM
mr fantastic
Quote:

Originally Posted by a69356
Hello everyone,

what is the difference between the Binomial distribution and Poisson distribution and Under which scenarios we can use Binomial distribution and Poisson distribution?

Any

Thanks,
Ashish