Well, the problem is that he does not replace the first marble after he draws it. Therefore, yes, he has a 2/12 probability of drawing a yellow marble first, but then he has a 4/11 probability of drawing a red marble second, not 4/12. This is because there are going to only be 11 marbles left in the bag after he draws the first marble and does not replace it.
The correct answer would be:
(2/12)(4/11)=8/132=4/66=2/33
We are looking for the inner perimeter of the track. Since there are two semicircles, these mix to form one full circle so we can use the formula to find the circumference of the circle with a diameter of 60 m, which was given to us. With a diameter of 60m, the radius will be 30m. Now we can solve this problem.
C = 2πr
C = 2π(30)
C = 60π
The semicircle ends of the track are a distance of 60π m, and now we just need to add the lengths of the inner track which are 100 m each. So:
P = 60π + 100m + 100m
P = 200 + 60π
P = 388.5 m
The right answer is
0.627
