Guy Berger Posted October 30, 2006 Report Posted October 30, 2006 So today I go into an interview. The first half goes great. Then the guy decides to offer me some choice brain-teasers. "Let's say I give you 99 numbers between 1 and 100. How do you figure out which one is missing?" "Calculate the probability that in a group of 20 people, at least two have the same birthday." etc. I got every. single. one. of. them. wrong. Alright, maybe that wasn't that funny but I was laughing after I left. Guy Quote
7/4 Posted October 30, 2006 Report Posted October 30, 2006 "Let's say I give you 99 numbers between 1 and 100. How do you figure out which one is missing?" Slap it on a spreadsheet and sort it. Look for missing number. I was looking at IQ test a few weekends ago. Pretty interesting questions. I'd forgotten all about the IQ tests I'd taken in my teens. Quote
rockefeller center Posted October 30, 2006 Report Posted October 30, 2006 "Let's say I give you 99 numbers between 1 and 100. How do you figure out which one is missing?" Slap it on a spreadsheet and sort it. Look for missing number. Or maybe something like (n*(n+1))/2 - sum of the given numbers (one missing)? Quote
Robert J Posted October 30, 2006 Report Posted October 30, 2006 I was asked this one: "How many gas stations are there in Canada?" Quote
Guy Berger Posted October 30, 2006 Author Report Posted October 30, 2006 "Let's say I give you 99 numbers between 1 and 100. How do you figure out which one is missing?" Slap it on a spreadsheet and sort it. Look for missing number. Or maybe something like (n*(n+1))/2 - sum of the given numbers (one missing)? Good answer. Now let's say I give you 98 numbers. How do you figure which two are missing? I think calculating the number of gas stations in Canada would be doable as long as only a "reasonable" answer was expected. Guy Quote
7/4 Posted October 30, 2006 Report Posted October 30, 2006 I was asked this one: "How many gas stations are there in Canada?" yes. Quote
rockefeller center Posted October 30, 2006 Report Posted October 30, 2006 "Let's say I give you 99 numbers between 1 and 100. How do you figure out which one is missing?" Slap it on a spreadsheet and sort it. Look for missing number. Or maybe something like (n*(n+1))/2 - sum of the given numbers (one missing)? Good answer. Now let's say I give you 98 numbers. How do you figure which two are missing? The "one number is missing" method obviously won't work (2 + 4 = 1 + 5) but I'd still employ it... Missing: 70, 13 5050 - 4967 = 83 -> missing numbers < 83 Finde one missing number: 82, 81, 80, ... 70 83 - 70 = 13 Missing numbers: 70, 13 Can't come up with an elegant algorithm. Do you know one? Quote
J Larsen Posted October 30, 2006 Report Posted October 30, 2006 So today I go into an interview. The first half goes great. Then the guy decides to offer me some choice brain-teasers. "Let's say I give you 99 numbers between 1 and 100. How do you figure out which one is missing?" "Calculate the probability that in a group of 20 people, at least two have the same birthday." etc. I got every. single. one. of. them. wrong. Alright, maybe that wasn't that funny but I was laughing after I left. Guy I'm guessing this was a consulting firm or an I-bank. I had a few interviews like that, including the one for my current job. I screwed up a very basic probability question (something like "If you test positive for a disease two out of three times, and the test gives false positives 60% of the time and false negatives 5% of the time, what is the probability you have the disease... c'mon, we don't have all day..."), but was still hired. (Who knows, maybe it cost me a few grand a year, though...) Quote
Ken Dryden Posted October 30, 2006 Report Posted October 30, 2006 I remember going to meet a man named Harv Taratoot for job interview. I was staring straight ahead and was surprised when he opened the door and was easily a foot shorter than me, causing me to quickly awkwardly redirect my gaze forward. I made it through another round of interviews with him, but didn't get the job. Quote
Randy Twizzle Posted October 30, 2006 Report Posted October 30, 2006 File this under traumatic job interview When I was a high school junior a friend arranged for me to get a job at the drive-in movie snack bar where he worked. All I had to do was go to the drive-in, fill out an application, meet the manager and the job was mine. I dutifully filled out the form and met the manager who started to explain what the job entailed. About half way through his spiel, he stopped and angrily asked me why I was laughing at him (I wasn't), ripped my application in half and told me to get the hell out before he punched me in the mouth. The next week he told my friend that maybe he had misjudged me and if I wanted to reapply he'd meet with me again. I declined. Quote
Jazzmoose Posted October 30, 2006 Report Posted October 30, 2006 I was asked this one: "How many gas stations are there in Canada?" Is that what y'all call Tim Horton's now? Quote
Hot Ptah Posted October 30, 2006 Report Posted October 30, 2006 (edited) In my interviews a man from Chicago said, "I just can't believe that anyone who grew up in Wisconsin could fit in and live in Chicago. You have 20 seconds to tell me how you could." I thought I gave a convincing answer but it did not suit him. I remember that he had rings on every finger, most with gemstones. Another time a guy said, "if you are well suited to this job you will love doing puzzles. Do you love puzzles?" Of course I said yes. Then he said, "well then, if you are suited to this job you will get this puzzle right away." He went on and on with a very complicated word problem, which I could not follow for the life of me. At the end he said excitedly, "O.K.! What is the answer to...THE PUZZLE!" I tried my best to put a good face on the fact that he was talking a foreign language to me. It did not work. Edited October 30, 2006 by Hot Ptah Quote
Robert J Posted October 31, 2006 Report Posted October 31, 2006 I was asked this one: "How many gas stations are there in Canada?" Is that what y'all call Tim Horton's now? Many gas stations have a Tim's attached. I guessed 10,000. Believe it or not - it was to be a piano teacher at a music school! They hired me as a salesperson instead. Quote
Guy Berger Posted October 31, 2006 Author Report Posted October 31, 2006 (edited) Good answer. Now let's say I give you 98 numbers. How do you figure which two are missing? The "one number is missing" method obviously won't work (2 + 4 = 1 + 5) but I'd still employ it... Missing: 70, 13 5050 - 4967 = 83 -> missing numbers < 83 Finde one missing number: 82, 81, 80, ... 70 83 - 70 = 13 Missing numbers: 70, 13 Can't come up with an elegant algorithm. Do you know one? Well, there is an "elegant" algorithm. (I put elegant in quotes because only mathematicians would think it so. The rest of us would just go through the numbers one by one and do it more quickly.) Calculate 100 factorial. Then calculate the product of all 98 numbers on the list. The quotient is the product of the two missing numbers. Now you have a system of two equations in two variables and you can easily solve for the missing numbers. How did I fail to come up with this idea in my interview? J Larsen -- this was in fact an interview for a consulting firm. Randy and Hot Ptah -- I enjoyed your stories! Guy Edited October 31, 2006 by Guy Quote
Guy Berger Posted October 31, 2006 Author Report Posted October 31, 2006 I guessed 10,000. Believe it or not - it was to be a piano teacher at a music school! They hired me as a salesperson instead. I think that is an excellent guess! Guy Quote
GA Russell Posted October 31, 2006 Report Posted October 31, 2006 "Let's say I give you 99 numbers between 1 and 100. How do you figure out which one is missing?" I'd have first said, "There are only 98 numbers between 1 and 100." Quote
Jazzmoose Posted October 31, 2006 Report Posted October 31, 2006 "Let's say I give you 99 numbers between 1 and 100. How do you figure out which one is missing?" I'd have first said, "There are only 98 numbers between 1 and 100." I'll bet you'd have got the job! Quote
rockefeller center Posted October 31, 2006 Report Posted October 31, 2006 Good answer. Now let's say I give you 98 numbers. How do you figure which two are missing? The "one number is missing" method obviously won't work (2 + 4 = 1 + 5) but I'd still employ it... Missing: 70, 13 5050 - 4967 = 83 -> missing numbers < 83 Finde one missing number: 82, 81, 80, ... 70 83 - 70 = 13 Missing numbers: 70, 13 Can't come up with an elegant algorithm. Do you know one? Well, there is an "elegant" algorithm. (I put elegant in quotes because only mathematicians would think it so. The rest of us would just go through the numbers one by one and do it more quickly.) Calculate 100 factorial. Then calculate the product of all 98 numbers on the list. The quotient is the product of the two missing numbers. Now you have a system of two equations in two variables and you can easily solve for the missing numbers. D'oh. Thanks, Guy. Quote
Epithet Posted November 1, 2006 Report Posted November 1, 2006 "Let's say I give you 99 numbers between 1 and 100. How do you figure out which one is missing?" So what's the answer they wanted? Another nomination for 5050 - sum. Quote
(BB) Posted November 1, 2006 Report Posted November 1, 2006 OK, since we have some math-heads in the room, can someone explain to me how this problem works. 3 men are getting a hotel room and the guy at the desk says, $30.00 so they each kick in $10. The manager comes back and tells the desk clerk that the room they rented was only a $25.00 room and to take them their change. He figures that rather than making change he will give them each back $1.00 and keep the extra $2.00 for his hard work. So now each man has paid $9.00 (x3 =$27.00) and the clerk has $2.00 What happened to the other dollar? Sorry, no job offers if you can explain it. Bill Quote
Aggie87 Posted November 1, 2006 Report Posted November 1, 2006 (edited) I like that challenge. If you consider that $2 in effect a tip (I'm not sure what service was actually rendered, though), then the men actually handed over $28 in cash for the room itself. Since the cost of the room was $25, their change was $3 ($1 of which went back to each person). No missing dollar when you look at it that way. They each paid $8.33 for the room, plus $0.67 tip to the clerk, for a total of $9.00. Edited November 1, 2006 by Aggie87 Quote
(BB) Posted November 1, 2006 Report Posted November 1, 2006 I see that the math works if you start from the $30 and subract tip $2 and cost of the room at $28. What I don't get, or can't figure out the error in my reasoning is why when you look at from the point of view if the guests it doesn't add up. Guest A pays $10 gets $1 back = $9 paid Guest B pays $10 gets $1 back = $9 paid Guest C pays $10 gets $1 back = $9 paid Total $27 + $2 tip =$29 I know the error is in my logic, I just can't figure out what mistake I am making. My brother-in-law, who teaches math, loves to taunt me with this. Thanks, Bill Quote
Aggie87 Posted November 1, 2006 Report Posted November 1, 2006 They didn't pay $27 + $2, they paid a total of $27 (ok they paid $30 and got $3 back). The $27 included the $2 tip. Quote
Guy Berger Posted November 1, 2006 Author Report Posted November 1, 2006 OK, since we have some math-heads in the room, can someone explain to me how this problem works. 3 men are getting a hotel room and the guy at the desk says, $30.00 so they each kick in $10. The manager comes back and tells the desk clerk that the room they rented was only a $25.00 room and to take them their change. He figures that rather than making change he will give them each back $1.00 and keep the extra $2.00 for his hard work. So now each man has paid $9.00 (x3 =$27.00) and the clerk has $2.00 What happened to the other dollar? Sorry, no job offers if you can explain it. Bill There is no "other dollar". The $2 comes out of the $27. Guy Quote
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