Varsha lives alone and dislikes cooking, so she goes out for dinner every evening. She has two favourite restaurants, Dosa Paradise and Kababs Unlimited, to which she travels by local train. The train to Dosa Paradise runs every 10 minutes, at 0, 10, 20, 30, 40 and 50 minutes past the hour. The train to Kababs Unlimited runs every 20 minutes, at 8, 28 and 48 minutes past the hour. She reaches the station at a random time between 7:15 pm and 8:15 pm and chooses between the two restaurants based on the next available train. What is the probability that she ends up eating in Kababs Unlimited?

(A) 1/5 

(B) 1/3 

(C) 2/5

(D) 1/2

Responses

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karmjitjoshi's picture

Train timings for Dosa Paradise

7:20 ,7:30, 7:40, 7:50, 8:00, 8:10

Train timings for Kabab Unlimited.

7:28, 7:48, 8:08

Favourable time slots

7:20-7:28  = 8 minutes
7:40-7:48 = 8 minutes
8:00-8:08 =8 minutes.

Probability= 24/60 = 2/5

why we have taken the time slots here why not 3/9= 1/3 ?

sujitchowdhury's picture

i also have same doubt ..

I believe the reason is that if she reaches the station at 7.20 or 7.21, she'll miss the first train so to end up getting a train for kabab unlimited, we have a time slot of 8 minutes. Similar concept can be applied to the other cases. 

Let me know if I am correct

pritam's picture

Very nice question. Must attempt.

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