Question: The probability of a car passing a certain intersection in a 20 minute windows is 0.9. What is the probability of a car passing the intersection in a 5 minute window? (Assuming a constant probability throughout)
Answer: This is one of the basic probability question asked in a software interview. Let’s start by creating an equation. Let x be the probability of a car passing the intersection in a 5 minute window.
Probability of a car passing in a 20 minute window = 1 – (probability of no car passing in a 20 minute window)
Probability of a car passing in a 20 minute window = 1 – (1 – probability of a car passing in a 5 minute window)^4
0.9 = 1 – (1 – x)^4
(1 – x)^4 = 0.1
1 – x = 10^(-0.25)
x = 1 – 10^(-0.25) = 0.4377
That was simple eh. Ready for a challenge? Have a look at some of the other probability questions.
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Blog looks really good mate, keep it up! The information is delivered solidly!
Isn’t this only valid if ‘a car passing by’ is meant to mean ‘one or more cars passing by’ instead of ‘exactly one car passing by’?
That is a valid point. I guess I should have phrased the question as “at least one car passing by”.