Due to construction, the speed limit along an 8-mile section of highwa

Question

Due to construction, the speed limit along an 8-mile section of highway is reduced from 55 miles per hour to 35 miles per hour. Approximately how many minutes more will it take to travel along this section of highway at the new speed limit than it would have taken at the old speed limit ?

(A) 5
(B) 8
(C) 10
(D) 15
(E) 24

PS21149

(A) 5
 (B) 8
 (C) 10
 (D) 15
 (E) 24

PS21149

fluke · Accepted Answer

Old time in minutes to cross 8 miles stretch = 8*60/55 = 8*12/11 = 96/11= 8.72
New time in minutes to cross 8 miles stretch = 8*60/35 = 8*12/7 = 13.71

Time difference = 13.71-8.72= 5

Ans: "A"

gmat1220 · Answer

Let t1 is time taken @ 55 mph 
t1 = 8/55
Let t2 is time taken @ 35 mph 
t2 = 8/35
Difference in time = 8/35 - 8/55 = 8 * 20 / (35 * 55) hr = 160 * 60 / (35 * 55) mins = 4.7 = 5 (approx) mins

subhashghosh · Answer

8/35 - 8/55 = 8/5 * ( 11 - 7)/77

= 8/5 * 4/77 * 60 min

= 8 * 12 * 4/77

= 384/77 ~ 4.9

Answer - A

gmat1220 · Answer

I wondering if someone can use componendo / dividendo since t1/t2 is known. Hence average speed and average time can come into picture. Otherwise there is no takeaway from this problem.

Spidy001 · Answer

8/35 - 8/55 ~= 5

Answer is A.

beyondgmatscore · Answer

Since answer choices are fairly dispersed, we can use approximations here.

Difference is given by  8*60/35 - 8*60/55

We can substitute 36 instead of 35 and 54 instead of 55 in expression above without sacrificing accuracy too much

We will get  8*10/6-8*10/9 = 8*10*(1/6-1/9) = 8*10/18  ~4.5 ~5

ravsg · Answer

=>55 x t1 = 35 x t2
=>t2 = 11/7 x t1
=> t2- t1 = 4/7 t1 = 4 x 8 / (7 x 55)
=> 1/16 (approx) hours
1/10 hrs is 6 mins, and 1/20 hr is 3 mins so 1/16 is around 4 and 5
Ans = A

GMATGuruNY · Answer

Original time in minutes =  \frac{d}{r} * 60 = \frac{8}{55} * 60 = \frac{8}{11} * 12 ≈ 9  minutes.

\frac{new-speed}{original-speed} = \frac{35}{55} = \frac{7}{11} 
Since the rate and time have a reciprocal relationship:
 \frac{new-time}{original-time} = \frac{11}{7} ≈ \frac{3}{2}

The resulting time ratio indicates that the new time is about 50% greater than the original time.
Thus:
Time increase in minutes ≈ 50% of 9 = 4.5.

A

Jsound996 · Answer

Because we're trying to find the difference in approximate minutes it would take with the new vs old speed, we can use estimation
We are trying to find New Time - Old Time = X

Since we're dealing with Rates and Distance; Use the formula Rate * Time = Distance

Old speed limit: 55 mph * T1 = 8

T1 =  \frac{8}{55} * 60  minutes, we need to multiply by 60 to get it in mins

T1  \frac{480}{55}  minutes

New speed limit: 35 mph * T1 = 8

T2 =  \frac{8}{35} * 60  minutes, we need to multiply by 60 to get it in mins

T2  \frac{480}{35}  minutes

This is where estimation comes in handy:

T1  \frac{480}{55}  minutes, we know that 55*10 = 550 mins, and 55*9 = 495. So T1 is approx 9 mins

T2  \frac{480}{35}  minutes, we know that 35*10 = 350. You can subtract 480 - 350 = 130. 35 can go into 130 around 4 times (35*4 = 140). So 10 + 4 = approx 14 mins

~14 - ~9 = Approx 5

So the ANSWER IS A

Basshead · Answer

distance = rate * time

distance/rate = time

\frac{8}{55} * 60 = \frac{96}{11} = 9  minutes

\frac{8}{35} = \frac{96}{7} = 14  minutes

14 - 9 = 5  minutes

Answer is A.

Kinshook · Answer

Given: Due to construction, the speed limit along an 8-mile section of highway is reduced from 55 miles per hour to 35 miles per hour. 
Asked: Approximately how many minutes more will it take to travel along this section of highway at the new speed limit than it would have taken at the old speed limit ?

Change in time required to travel along the section of highway = (8/35 - 8/55)*60 = (8/7 - 8/11)*12 = (11-7)8*12/77 = 4*8*12/7*11 ~ 5 minutes
 
IMO A

DmitryFarberMPrep · Answer

Quick approximation:

55 mph is almost 1 mile/minute. So at that speed, the trip takes just over 8 minutes. 35 mph is more than half the original speed, so a trip at that speed will take less than double the original time. That means the increase is less than 8 minutes, so A.

RahulJain293 · Answer

Since the fractions are a bit tedious, I made one assumption.

- Let the distance be 80 miles instead of 8 miles.

Case 1 = @55 mph
Time = 80/55 gives 1.4 hours & for 8 miles we shift a decimal 0.14 hours

Case 2 =  35  mph
Time = 35/55 gives 2.2 hours & for 8 miles we shift a decimal 0.22 hours

Here the difference in 0.22 & 0.14 hours gives the time saved (i,e, 0.08 hours)
0.08 hours is nothing but 8% of 60 minutes and basically any number less than 10% i.e 6 minutes.

Hence answer is A = 5 minutes.

DanTheGMATMan · Answer

Classic distance problem- subtract the times:

https://www.youtube.com/watch?v=18opcUml4iI

Sa800 · Answer

why cant i do this by stating that since cars are going 20 mph Slower that means 8/20 is the time in hours that was slowed down…?

DmitryFarberMPrep · Answer

Because the difference in time actually depends on the actual speed, not just the difference in speed. Consider a few cases:

10 miles 10 miles/hr takes 1 hr = 60 min 
10 miles 20 miles/hr takes 1/2 hr = 30 min
10 miles 30 miles/hr takes 1/3 hr = 20 min
10 miles @ 40 miles/hr takes 1/4 hr = 15 min

Do you see the pattern? The faster you're going, the less of a difference it makes to increase your speed by a given amount. This is why really fast runners often differ in their times by very small amounts. If you're running at only 4 miles/hr and you increast to 5 miles/hr, you take three whole minutes off your mile time (15 min --> 12 min). If you're running 12 miles/hr (5-min mile), going up to 13 miles/hr only takes about 23 seconds off your mile time. You have to go up to 15 mph to take a full minute off.

KarishmaB · Answer

Ratio of speeds = 55: 35 = 11:7 Ratio of time taken = 7 : 11 So if 7 mins were taken on that stretch before, now 4 extra minutes will be taken. If 14 mins were taken on that stretch before, now 8 extra minutes will be taken etc. Let us calculate exactly how many minutes were taken on that stretch before. Time taken in minutes at speed 55 mph = 8*60/55 = a bit more than 8 Hence the extra time taken will be around 5. No other option comes close. Answer (A) Check this video for a discussion on TSD using ratios: https://youtu.be/7ASEIvxYPCM

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Due to construction, the speed limit along an 8-mile section of highwa

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