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Quantitative Developer Interview Questions


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How to measure 9 minutes using only a 4 minute and 7 minute hourglass

17 Answers



The key is understanding that you will have to use the two hourglasses together. Since this problem could be asked in many ways using different values for the hourglasses and the total amount of time, it's more important to understand how you use the tools rather than memorize a specific example. The question is used to determine those who can apply their knowledge to solve problems vs. those who memorize answers "from the book". Start both timers. After four minutes, the four-minute timer will have expired and the seven-minute timer will have three minutes remaining. Flip the four minute timer over. After seven minutes, the seven-minute timer will have expired and the four-minute timer will still have one minute left. Flip the seven-minute timer over. After eight minutes, the four-minute timer will have expired for the second time. The seven-minute timer will have accumulated one minute after it's last flip. Flip over the seven-minute timer and when it expires nine minutes will have elapsed. For extra measure, you can always throw in something like, "assuming the timers can be flipped over nearly instantly..."

How many numbers between 1 and 1000 contain a 3?

13 Answers

You have a chest of 8 drawers. With probability 1/2, you put a letter in one of the drawers. With probability 1/2, you don't put a letter in any drawer. I open the first 7 drawers, all are empty. What is the probability there is a letter in the 8th drawer?

9 Answers

If you toss a coin n times, what's the expected value of n if you get the 2nd head?

6 Answers

Given a m*n matrix with values -1 or 1, try to flip the values in a given row and a given line efficiently.

3 Answers

What is the probability of an integer from 1 to 60,000 not having the digit 6?

5 Answers

There were bunch of ridiculously difficult probability questions and computer science algorithm questions. Nothing worth to mention here

2 Answers

There are 50 noddles in a bowl. Each time you randomly select two ends of the noddles from the bowl and tie together. What is the expected number of loops formed from this process?

3 Answers

Implementing the LRU algo

2 Answers

keep throw a coin if two head A will win if first is head second is tail B will win, keep throwing until have a winner. who has better chance to win?

2 Answers
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