What is the probability that there are at least 2 more high risk drivers than low ris

[pitwen]

Among a pool of adults drivers:
50% are low risk driver, 30% are moderate risk and 20% are high risk driver.

An insurance writes 4 new policy for adults. What is the probability that there are at least 2 more high risk drivers than low risk drivers?

I made use pf the trinomial distribution that is:
4!/0!2!2! (0.5)^0(0.3)^2(0.2)^2 + 4!/1!0!3! (0.5)^1(0.3)^0(0.2)^3 +4!/0!0!4! (0.5)^0(0.3)^0(0.2)^4 = 0.0552

However, the answer wasn't correct. Why?:geek:

[NoMoreExams]

Among a pool of adults drivers:
50% are low risk driver, 30% are moderate risk and 20% are high risk driver.

An insurance writes 4 new policy for adults. What is the probability that there are at least 2 more high risk drivers than low risk drivers?

I made use pf the trinomial distribution that is:
4!/0!2!2! (0.5)^0(0.3)^2(0.2)^2 + 4!/1!0!3! (0.5)^1(0.3)^0(0.2)^3 +4!/0!0!4! (0.5)^0(0.3)^0(0.2)^4 = 0.0552

However, the answer wasn't correct. Why?:geek:

That's how SOA does it... maybe you have a calculation error. Have you looked through the SOA problems and SOLUTIONS?

[pitwen]

Woopz..i didn't know there is a solution set attached!!!
sorry@@

[Kenneth]

I think one of the major benefits of this forum is that you find out about the resources that everyone else has easy access to.

[pitwen]

agreed!!! the solutions set just helped me soooo much~~~ thanks!!!:tongue:

[claytonmccandless]

you forgot the chance that there would be 3 high and 1 moderate.