Posted by **Mattie** on Wednesday, May 25, 2011 at 9:47am.

a woman standing on a bridge overlooking a major insterstate wants to know how likely it is that the next 20 out of 50 cars that pass under the bridge are red cars, if she has observed in the past that the probability than any given car on that interstate highway is red is approximately 0.28.

What is the probability?

- STATS -
**drwls**, Wednesday, May 25, 2011 at 10:20am
Your question is worded in a confusing way. It sounds like the next 20 cars IN A ROW would have to be red. That would be a very low probability, (0.28)^20 = 8.8*10^-12, and the 30 cars seen after that would not matter.

Don't you mean that you want the probability that exactly 20 of the next 50 will be red?

That probability is

P(20) = (0.28)^20*(0.72)^30^50!/[30!*20!]

= 0.0217

The most likely number of red cars out of 50 would be 14. That probability is

P(14) = (0.28)^14*(0.72)^36* 50!/[14!*36!] = 0.1248

=

## Answer This Question

## Related Questions

- Math - The underside of a bridge has a shape of a parabolic arch. It has a ...
- physics - James Bond is trying to jump from a bridge and land on the first car ...
- Physics - James Bond is trying to jump from a bridge and land on the first car ...
- algebra - You live under a bridge that goes over a river. the underneath side of...
- algebra - You live under a bridge that goes over a river. the underneath side of...
- Stats/Probability - If 23% of the cars that pass by your house each day are red...
- Math-soh cah toa - A bridge is 140m long.From the ends of the bridge, the angles...
- math - There are 25 cars in a parking lot. Nine of the cars are red. The rest ...
- Math - trigonometry - A bridge is 70m long. From the ends of the bridge the ...
- Math - The bar graph below shows the numbers of various colors of cars owned by ...

More Related Questions