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Pastimes : Logic Puzzles and Brain Teasers -- Ignore unavailable to you. Want to Upgrade?

To: R Jennings who wrote (30)	3/3/1998 3:36:00 AM
From: Chip Anderson	Respond to of 193

Good one! That's one approach - roughly estimate the size of the drainage basin and then guestimate the average amount of rainfall per hour. Sure, it's a rough estimate but that's all we're after here. My estimates (totally off the top of my head) - the US is ~2000 miles wide - the basin is roughly half the width of the US (more at the top, less at the bottom) - thus I'd estimate the basin at 1000 square miles - I don't know why but I think I recall that the average precipitation in year for Atlanta is 44 inches (which is higher than average) so let's say the average for the basin is 36 inches per year or 3 inches a month or .1 inch a day or .1/24=~0.004 inches an hour. - Now if I remember right, (I swear folks, I'm doing this off the top of my head!) that 0.004 inches of water is spread over a one square inch area. How many square inches in 1000 square miles? Lessee... 1 mile = ~5300 feet. 530012 = 63600 inches. 63600^2 = 4,044,960,000 square inches (phew!) So that's ~4 billion 0.004 = 16 million cubic inches of water per hour flowing into the basin on average every hour. As Mitch correctly pointed out, the net change of inflow to outflow must be zero or we lose the river so THEREFORE... 16 million cubic inches (or 1.3 million cubic feet) of water per hour roughly flowing out the mouth of the Mississippi every hour. TADA! (Does anyone have an authoritative source handy to see if I'm even close to reality?) Side note: The point of any _good_ interview question (and there are lots of bad ones out there) is the get the candidate to think and then talk through the thought process so that others can collaborate with them on the answer. A _great_ question does that in an unexpected way that throws the candidate _slightly_ off guard so more of the thinking process is exposed. (All IMHO of course) Now, bonus points for anyone who can come up with the other, totally different approach to answering this same question. Chip coolhistory.com