Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Every day, the number of traffic accidents has a distribution (probability mass function)

x    0    1    2    >2
P(x) 0.6  0.2  0.2  0

independently of other days. What is the probability that there are even more accidents on Friday then on Thursday?

This is a practice exam problem so the exact answer isn't as helpful as the proper solution.

share|improve this question
add comment

1 Answer

There is nice symmetry to exploit. Let $p$ be the probability of "more on Friday." Then $p$ is also the probability of more on Thursday. And $2p+e=1$, where $e$ is the probability the number of accidents is the same.

Once we know $e$, we will know $p$.

The probability the number of accidents is the same is the probability they are both $0$, plus the probability they are both $1$, plus the probability they are both $2$.

The probability they are both $0$ is $(0.6)^2$. Continue.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.