Here's another method that allowed me to solve the question in approximately 30 seconds:

20 miles per hour translates to traveling 1 mile every 3 minutes. Since the bridge is longer than 1/2 mile but shorter than 1 mile, the answer must be between 1.5 and 3 minutes. The only answer choice that fits this range is 2 minutes.

First, convert the speed to feet per minute.

20 miles per hour = ( 20 * 5280 ) feet per 60 minutes.

Time = \(\frac{Distance}{Speed}\) = \(\frac{4024}{(20 * 5280 ) / 60}\) = \(\frac{4024 *60}{20 * 5280}\) = \(\frac{4024 * 3}{5280}\) = \(\frac{4024}{5280}\)*3

\(\frac{4024}{5280}\) < 1. Therefore, Time < 3.

We can eliminate (A) because \(\frac{4024}{5280}\) is not equal to \(\frac{1}{3}\). The only answer choice remaining is (B). Therefore, (B) is the answer.

Does anyone have a tip for a quick way to solve the division of 4024/5280? This is where I spend the majority of my time on the problem and am wondering if I can do something faster. I do a lot of trial and error.

Hi amandakay,

The GMAT would never expect you to calculate the exact value of 4024/5280, so if you're ever thinking about doing something so "calculation heavy", then there's almost certainly a faster or easier way to get to the correct answer. In this prompt, you should notice the word "approximately" - that means that you DON'T have to calculate that fraction, but you do have to estimate the value.

If we 'round down', then 4024 ft./5280 ft. is a little less than 4/5 of a mile. Knowing THAT, and that 20 mph is 1 mile every 3 minutes, can you correctly answer the question?

GMAT assassins aren't born, they're made,
Rich
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hello friends

here is a quick way to solve it

if 20 miles = 60 min---> then 1 mile = 3 min

if length of bridge (4,024 feet) is shorter than 1 mile (5,280 feet)

then only option is B

The length of the bridge, in miles, is:

4,024/5,280 = 503/660, which is about 500/660 = 50/66 = 25/33.

Using the formula: time = distance/rate, we see that the time, in hours, is:

[25/33]/20 = 25/(33 x 20) hours

So the time in minutes is:

25/(33 x 20) x 60 = (25 x 3)/33 = 25/11, which is about 2 minutes.

Answer: B
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