Probability Question---Please HELP

[mikep30]

The local train station reports that70% of all arriving trains are on time. Using the table of randomly generated numbers below, let 0,1,2,3,4,5, and 6 represent an on-time arrival, and 7,8, and 9 represent a late arrival.
What is the probability that the next two trains will be on time?


25 71 87 46 66 13 63 36 01 59
27 07 83 25 72 24 73 52 59 81
14 09 40 64 81 72 02 38 21 09
92 10 97 34 36 45 53 18 23 78


a. 3/40 b. 9/40

c. 19/40 d. 21/40



*Please explain***

 

[tkhunny]

What did you get? You have 80 random numbers. How many are 7, 8, or 9? I get 21 of the 80 values.

What is the probability that the next train will be on time, given that all other trains do not change the delivery?

 

[mikep30]

What did you get? You have 80 random numbers. How many are 7, 8, or 9? I get 21 of the 80 values.

What is the probability that the next train will be on time, given that all other trains do not change the delivery?

I'm still confused. How did you get 21? Could you please explain.:-?

 

[mikep30]

I think I may have figured this out. Let me know if I'm correct. If each train has a 70% chance of arriving on time, then that equates to the 7 out of the 40. Therefore, this train and the next two trains each has 7 out of 40. Thus, giving me 21 out of 40.

 

[tkhunny]

What?! Where did you get 70%? How did that turn into 7/40? Did you use a magic wand to turn that into 7/21?

Show your work! So far, it looks like you are just throwing darts.

They are random numbers. Count them. How many are 7, 8, or 9?

 

[mikep30]

I don't have any work to show. All I know is that this is a simulation problem and I thought that the 40 random numbers may have represented the whole (100%) of the trains. When I count the actual digits 7,8, and 9, I don't get 21. Furthermore, if I add the digits in each set, I still don't get 21. Could you SOMEONE please explain this problem in detail.