[A] Question 3: Easy algebra

Probability Level 3

You are standing beside a road.

The probability that you don't see a car pass by after 30 mins is 5%

Find the probability that you don't see a car pass by after 10 mins.

Notes:

A calculator is allowed.

Round your answer to three decimal places.


The answer is 36.840.

Tan Wee Kean by Tan Wee Kean , 20, Singapore

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1 solution

Tan Wee Kean
Sep 20, 2014

Let the probability of not seeing a car pass by after 10 mins be x%

Then the probability of not seeing a car pass by after 30 mins is

( x 100 ) 3 = 5 100 { (\frac { x }{ 100 } ) }^{ 3 }=\frac { 5 }{ 100 }

Punch in some buttons in your calculator and you get x = 36.840..... x=36.840.....

I think the main problem here is that some are equating percentage as follows:

x 3 = 5 { x }^{ 3 }=5

Think about it: why is it wrong?

2 Helpful 0 Interesting 0 Brilliant 0 Confused

Thanks. I've updated the phrasing of the problem to match your solution.

I've updated the answer so that those who previously entered 0.36480 were marked correct.

Note that you made the very mistake that you were trying to warn against. You asked for the probability (which is between 0 and 1), as opposed to the percentage probability.

Calvin Lin Staff - 6 years, 8 months ago

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