# Probability

• May 4th 2008, 02:14 PM
shogunhd
Probability
Let X denote the numebr of flaws along an 100m reel of magnetic
tape. If in average there are 25 flaws every 100m of tape find the
probability that a random 200m tape contains more than 30 flaws.
• May 4th 2008, 07:01 PM
mr fantastic
Quote:

Originally Posted by shogunhd
Let X denote the numebr of flaws along an 100m reel of magnetic
tape. If in average there are 25 flaws every 100m of tape find the
probability that a random 200m tape contains more than 30 flaws.

Use the Poisson distribution.
• May 4th 2008, 07:23 PM
shogunhd
Quote:

Originally Posted by mr fantastic
Use the Poisson distribution.

Thank you. So my lambda in this case is 25 and the probability of being more than 30 = 1 - Pr(x<=30) in the Poisson distribution.
• May 4th 2008, 10:16 PM
mr fantastic
Quote:

Originally Posted by shogunhd
Thank you. So my lambda in this case is 25 and the probability of being more than 30 = 1 - Pr(x<=30) in the Poisson distribution.

X is the random variable number of flaws in 100 m of tape.

X ~ Poisson $(\mu_X = 25)$.

But you want Pr(Y > 30) where Y = 2X. And $\mu_Y = 2 (25) = 50$ .....