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how to solve this problem in 2 mins. any easy method? [#permalink]
18 Jul 2011, 13:09

00:00

A

B

C

D

E

Difficulty:

5% (low)

Question Stats:

50% (02:10) correct
50% (01:48) wrong based on 6 sessions

X is planning a bus trip across town that involves three buses. Bus 1 travels between house and downtown, and leaves every half-hour starting at 7:20am. X will need to be on Bus 1 for 1 1/5 hours. Bus 2 travels between downtown and uptown every half-hour starting at 7:10am. X will have to be on Bus 2 for 2/3 hour. Lastly, Bus 3 travels between uptown and destination every hour starting at 9 Am. what is the least total amount of time X wmust spend waiting for buses, assuming all buses stay on schedule?

A. 12 mins B. 18 mins C. 48 Mins D. 1 hour 12 mins E. 1 hour 20 mins

Re: how to solve this problem in 2 mins. any easy method? [#permalink]
18 Jul 2011, 15:10

Second bus service starts 10 mins earlier than first bus service and both have same frequency (every 30 mins). First bus take 1hr 12 mins. Thus second bus one can get has waiting time 30 - (10+12)=8 mins It is same always. If you write time arrival time for first bus(8:32,9:02,9:32, add 30mins) and departure time for second bus(8:40,9:10,9:40 etc), you will get the same.

Similarly, third bus leaves every hour and service starts exactly on hour clock, a 10 mins early(7:10am and 9am, just mins since buses have frequency of either half or one hour) Also second bus takes 2 hour 40 mins Waiting time = 60-(10-40) =10 mins or 10+30=40 mins (since second bus leaves every 30 mins and third every 1hr)

First waiting time is always 8 mins, so take least time 10 mins for second waiting time. Thus, least waiting time = 8+10 = 18 mins.

It did take more than 2 mins though.
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Re: how to solve this problem in 2 mins. any easy method? [#permalink]
18 Jul 2011, 23:06

valencia wrote:

X is planning a bus trip across town that involves three buses. Bus 1 travels between house and downtown, and leaves every half-hour starting at 7:20am. X will need to be on Bus 1 for 1 1/5 hours. Bus 2 travels between downtown and uptown every half-hour starting at 7:10am. X will have to be on Bus 2 for 2/3 hour. Lastly, Bus 3 travels between uptown and destination every hour starting at 9 Am. what is the least total amount of time X wmust spend waiting for buses, assuming all buses stay on schedule?

A. 12 mins B. 18 mins C. 48 Mins D. 1 hour 12 mins E. 1 hour 20 mins

I go also go with C . 48 mints.. unless 2/3 reads as 7/6 in which case its 18 mints

Re: how to solve this problem in 2 mins. any easy method? [#permalink]
18 Jul 2011, 23:31

valencia wrote:

X is planning a bus trip across town that involves three buses. Bus 1 travels between house and downtown, and leaves every half-hour starting at 7:20am. X will need to be on Bus 1 for 1 1/5 hours. Bus 2 travels between downtown and uptown every half-hour starting at 7:10am. X will have to be on Bus 2 for 2/3 hour. Lastly, Bus 3 travels between uptown and destination every hour starting at 9 Am. what is the least total amount of time X wmust spend waiting for buses, assuming all buses stay on schedule?

A. 12 mins B. 18 mins C. 48 Mins D. 1 hour 12 mins E. 1 hour 20 mins

Re: how to solve this problem in 2 mins. any easy method? [#permalink]
19 Jul 2011, 00:39

So, we have to try 2 cenarois then, dint look at the Q stem, it states least wait time, how could one possibly think different. Fluke - you are an eye opener Thank You