Brain Teasers/Interview Questions

gerry87

I guess a few around here (like myself) might be looking for job interviews that ask probability questions's, thought it might be handy to have a brain teaser thread since it's more about whethe. So throw out your toughest!

Also if you have any tips for handle or go about these kind of q's, throw them out there too.

A lily pad is sitting in a pond, every day it doubles in size. After 30 days it covers the entire surface area of the pond. Now imagine the same pond with 8 lily pads, each the same size as the original one, that grow in the same manner. How many days will it take the 8 lily pads to grow to the surface area of the pond.

(is it better to have spoilers or not?)

ZorbaTehZ

30 - 8= 22 days?

Edit: x2

Actually I'm pretty sure that's wrong (took the easy way out extrapolated from 2.

I'm going with 27 days

locum-motion

ZorbaTehZ wrote: »

30 - 8= 22 days?

Edit: x2

Actually I'm pretty sure that's wrong (took the easy way out extrapolated from 2.

I'm going with 27 days

Yep, I agree with your second answer.

LeixlipRed

You start with a lily pad of x surface area. After one day it's expanded to 2x SA, 2 days it's 4x, etc, etc. So after 30 days it's (2^30)x which is the surface area of the pond. If you start with 8 lily pads of identical size you have 8x as you're lily SA at the start. 8x=(2^3)x. So you need another 27 doubles to get to 2^30. So 27 days as already pointed out above.

Pherekydes

Doesn't it depend on the shape of the pond and the pads?

If the pond and the pads were circular, 8 pads would equal the total area of the pond, but you could not get the circumferences to coincide, so there would be overlapping, and you would need another day.

If the pond and the pads were perfect squares, you could not divide the big square into 8 smaller squares of equal size.

Overthinking it?

LeixlipRed

Maybe not, in an interview situation they might be curious to see if you see any problems or alternatives to the seemingly obvious solution.

gerry87

Pherekydes wrote: »

Doesn't it depend on the shape of the pond and the pads?

If the pond and the pads were circular, 8 pads would equal the total area of the pond, but you could not get the circumferences to coincide, so there would be overlapping, and you would need another day.

If the pond and the pads were perfect squares, you could not divide the big square into 8 smaller squares of equal size.

Overthinking it?

That was something i thought when i heard it, but i changed it a little. The question asked how long will it take the 8 to grow to the surface area of the pond. I didn't say they had to completely cover the pond.

If you thought something like that in an interview would it be best to just answer what you think they're asking or point out the problems?

Anyway, another.

You and your room mate host a party and invite 10 other pairs of room mates (20 people total). You survey everyone at the party except yourself as to how many people they shook hands with. From the poll you find two things.

1. Nobody shook the same number of hands.
2. Nobody shook his/her room mates hand.

How many hands did your room mate shake?

Mellor

Lol at everyone over thinking the lily pads problem. Would be the method an employer would look for imo, lateral thinking > numbers route.

my answer would be;
1 lily becomes 8 after 3 days. So starting with 8 becomes 30 after 27 days, as its simply a 3 head head start

You and your room mate host a party and invite 10 other pairs of room mates (20 people total). You survey everyone at the party except yourself as to how many people they shook hands with. From the poll you find two things.

1. Nobody shook the same number of hands.
2. Nobody shook his/her room mates hand.

How many hands did your room mate shake?

Hmm, I know how many hands each person shook, but not which one is the roommate, must be missing some link