A certain bridge is 4,024 feet long. Approximately how many minutes... : Problem Solving (PS)

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nalinnair

A certain bridge is 4,024 feet long. Approximately how many minutes does it take to cross this bridge at a constant speed of 20 miles per hour? (1 mile = 5,280 feet)

(A) 1
(B) 2
(C) 4
(D) 6
(E) 7

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.

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28 Feb 2021, 05:52

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Video solution from Quant Reasoning starts at 13:37
Subscribe for more: https://www.youtube.com/QuantReasoning? ... irmation=1

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26 May 2016, 21:59

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In this question unit of measurements have to be taken care of.

Distance: 4024 feet. This is (4024/5280) miles = 0.76 miles

Speed: 20 miles per hour

Time: (Distance / Speed) (0.76/20) {This will come in Hours}. Multiply by 60 to get answer in minutes. It is 2.28 minutes.

Answer to be 2 minutes.

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20 Mar 2017, 01:56

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nalinnair

A certain bridge is 4,024 feet long. Approximately how many minutes does it take to cross this bridge at a constant speed of 20 miles per hour? (1 mile = 5,280 feet)

(A) 1
(B) 2
(C) 4
(D) 6
(E) 7

distance = 4024 ft = 4024/5280 miles

time taken = 4024/5280*20 hours= 0.76 hours = 2.28 minutes close to 2 minutes

option B

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23 Jun 2017, 17:14

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Approximation!

D=4000
R=20mph
Convert it to miles per minutes = \(\frac{20}{60}\)
R = \(\frac{1}{3}\)

1 mile = approx 5000 feet

\(T=\frac{D}{R}\) \(=\frac{(4000*3)}{5000}\) \(=\frac{12000}{5000}\) \(=\frac{12}{5}\) = 2.4

Since the denominator is slightly more than 5000, the value will be less than 2.4.
i.e B

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nalinnair

A certain bridge is 4,024 feet long. Approximately how many minutes does it take to cross this bridge at a constant speed of 20 miles per hour? (1 mile = 5,280 feet)

(A) 1
(B) 2
(C) 4
(D) 6
(E) 7

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

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nalinnair

A certain bridge is 4,024 feet long. Approximately how many minutes does it take to cross this bridge at a constant speed of 20 miles per hour? (1 mile = 5,280 feet)

(A) 1
(B) 2
(C) 4
(D) 6
(E) 7

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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20 miles per hour = 3 miles/min

4024 / 5280 = 4000 / 5000 = 4/5

4/5 * 3 = 12/5 = 2 minutes

Answer is B.

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basshead

20 miles per hour = 3 miles/min

4024 / 5280 = 4000 / 5000 = 4/5

4/5 * 3 = 12/5 = 2 minutes

Answer is B.

Hi basshead,

Based on your various posts in the Quant forums, you are clearly a strong overall Quant thinker, but you have to be careful about the individual steps that you work through on each question that you face (since GMAT writers can often anticipate the type of little mistake that someone might make - and then the writers put the result of that mistake among the answer choices).

Here, 20 miles/hour is equivalent to 1 mile every 3 minutes (NOT 3 miles/minute).

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

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If they would have picked 3 min as an option, it would have been a little harder.

1/3 of a mile in 1 min
1/3 of 5280 feet is around 1750 feet
then 2 min = 3500 feet

And 4 min would be way too much.

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nalinnair

A certain bridge is 4,024 feet long. Approximately how many minutes does it take to cross this bridge at a constant speed of 20 miles per hour? (1 mile = 5,280 feet)

(A) 1
(B) 2
(C) 4
(D) 6
(E) 7

Getting math questions right without doing the math since 1999.

We can cover 20 miles per hour, so 1 mile every 3 minutes.
4024 feet is less than a mile, so we need an answer choice that's less than 3. C, D, and E are wrong.
4024 feet is more than half a mile, so we need an answer choice that's more than half of 3. A is wrong.

Answer choice B.

ThatDudeKnowsBallparking

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ScottTargetTestPrep

nalinnair

A certain bridge is 4,024 feet long. Approximately how many minutes does it take to cross this bridge at a constant speed of 20 miles per hour? (1 mile = 5,280 feet)

(A) 1
(B) 2
(C) 4
(D) 6
(E) 7

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

ScottTargetTestPrep
I decided to convert the rate...

I did (20 miles/1 hr)*(5280 ft/1 mile) --> 105,600 feet/1hr
I then set this up in my rt=d
(105,600 ft/1 hr)*(t)=4,024 ft

I then solved and approximated so the time = 4,024/105,600 --> 4,000/100,000 = 4/100
Then I converted to minutes (4/100)*60 = 2.4, and since i was dividing by ~105,000 before simplifying, the answer is even smaller than 2.4 --> 2 makes the most sense.

With this approach, I would be so appreciative to learn if you think that my work correct/efficient

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Given

Bridge = 4024 feet long
speed: 20 mph
1 mile = 5280 feet

Find
Time to cross the bridge

Approach

Convert 4024 to miles --> 4024 / 5280, I recognized that this is approximately 4 / 5, which is 0,8 miles
20 miles per 60 min
10 miles per 30 min
0,1 miles per 0,3 min --> 0,8 miles per 2,4 min, roughly 2 min

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nalinnair

A certain bridge is 4,024 feet long. Approximately how many minutes does it take to cross this bridge at a constant speed of 20 miles per hour? (1 mile = 5,280 feet)

(A) 1
(B) 2
(C) 4
(D) 6
(E) 7

easiest way to solve this is... 1 mile = 5280, given so 5280 multiply by 20
5280*20= 105600 this much dist we can cross with 20 ml/h , divide this with 60, 105600/60= 1760 feel cross in one min.
approximate ans we have to give so in given option 2 is only ans is there..

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