A question of time

Probability Level 4

Satvik and Agnishom decide to meet up at the library to discuss geometric probability. Each of them can reach the library at any random time between 4 pm and 5 pm.

They each decide to wait exactly 20 minutes for the other person or until 5 pm, whichever comes first.

The probability that they meet can be expressed as a b \dfrac{a}{b} , where a a and b b are positive co-prime integers. Find a × b a \times b .


The answer is 45.

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Satyen Nabar by Satyen Nabar , 48, India

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2 solutions

2 Helpful 1 Interesting 1 Brilliant 0 Confused

Great problem based on geometric probability!!

0 Helpful 0 Interesting 0 Brilliant 0 Confused

Why did you post this in the solution section. If you like the question then just hit the like button.

Arghyadeep Chatterjee - 3 years, 1 month ago

You can also draw a grid of the different axis representing either of them. From that partition the grid into 9 equal squares of side 20 mins.. If you look at the grids you should find that only 5 out of 9 give you the event of them meeting

Tshepiso Tsotetsi - 2 years, 4 months ago

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