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mlane25269
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This question requires a lot more calculation than we usually see on the GMAT.
We know time, we want to know if distance is greater than 6 miles.
(1) r > 16 feet per second
Let's start by swapping to miles per hour.
16 f/s = 16*3600 f/h = 16*3600/5280 m/h = 120/11 = approx 11mph
(we could also approximate 3600/5280 as roughly 3600/5400 = 2/3, and then 2/3(16) is between 11 and 12.)
So, minimum r is about 11. This means that:
minimum D = (min r)*t = 11(1/2) = 5.5
If the minimum distance is 5.5 miles, then D could be both lower and higher than 6: insufficient.
(1) r < 18 f/s
Same start:
18 f/s = 18*3600 f/h = 18*3600/5280 m/h = a bit more than 18(2/3) = a bit more than 12 mph.
So, maximum r is a bit more than 12. This means that:
maximum D = (max r)*t = a bit more than 12(1/2) = a bit more than 6.
Well, if maximum distance is more than 6, then actual distance could be both lower and higher than 6: insufficient.
Together: we know that 5.5 < D < a bit more than 6. So, it could still be both lower and higher than 6: insufficient.
