Not so fast

Algebra Level 2

Kevin was running a race and he is the 9th fastest and the 11th slowest. How many people were running the race?

21 19 20 22

Chung Kevin by Chung Kevin , 45, Australia

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2 solutions

Well actually there is a general formula for it.(which is derived from observation)

Let F r_ represent rank from the front and B r_ represent rank from bottom then we can say that Total number = F r + B r − 1 \text{Total number} = F_r + B_r - 1 .

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Hm, if we apply that to this problem, won't we get 11 + 9 = 20 11 + 9 = 20 ? The answer is actually 19.

Chung Kevin - 6 years, 4 months ago

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Sorry, it was a typo . *Edited

A Former Brilliant Member - 6 years, 4 months ago

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Looks good!

Chung Kevin - 6 years, 4 months ago
Akash Gupta
Jan 31, 2015

It is observed that...
There are 8 people faster than Kevin and 10 people slower than him and one is he himself.
Then, Total no. of people running = 8 + 10 + 1 =19

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