Simple maths logic problem

[nokia8650]

http://img372.imageshack.us/img372/2057/timezy9.jpg

See image above. The answer is D - 88, however I can only find 84! Please can someone let me know what I am missing:

20-7= 13
13*6 + 1 = 79 = total upto 2030
+ 2045 bus = 80

+ 4 buses (two in 21st hr, two in 22nd hr) = 84

Thanks

[HallsofIvy]

Looks straight forward to me. First there are the two morning runs. Then it runs "every 10 minutes" from 8:30 to 20:30 (8:30 A.M. to 8:30 P.M.). That's 12 hours and 6 times an hour for 12 hours is 72 times- actually 71 since we are counting exactly at 8:30 separately. Then 2 more runs until 21:14 (9:14 P.M.). Then 12 runs between 21:14 and 22:45 culminating in the final run. A total of 2+ 71+ 2+ 12+ 1= 88 runs.

[nokia8650]

Thanks for the reply. Isn't it every 10 minutes from 7:30 to 20:30, not from 8:30 to 20:30, which gives 79 runs up until the 20:30 run. Also, how are there "12 runs between 21:14 and 22:45 culminating in the final run?"

Thanks

[HallsofIvy]

I was interpreting "then every 10 mins" as meaning from the END of the first two runs. You are interpreting it as 10 min after the start of the second run. I can't say which interpretation is correct.