At time t measured in minutes after the beginning of the timed period,

Question

https://gmatclub.com/forum/download/file.php?id=38183 
At time t measured in minutes after the beginning of the timed period, which of the following gives the speed of the train in accordance with the table?

(A) t/6
(B) 10t
(C) 40 + t
(D) 40 + t/6
(E) 40 + 10t

shashaankbhat · Answer

IMO D.

I plugged in values for ‘t’ as 30 and as per graph speed is 45 for 30 mins.

D satisfies the condition

Posted from my mobile device

GMATSkilled · Answer

When using t = 0, A and B gives the speed as 0 but per table it's 40.
How to make it easy to choose, at speed t = 45, speed is a decimal and only option D would get you a decimal

Sent from my iPhone using GMAT Club Forum

animesh mohanty · Answer

For a difference of 30 mins the corresponding change in speed is 5, next we find that the change is proportional throughout ie t/6. so the speed of the train after time t is 40+ t/6 (D).

HG90 · Answer

Pls. Note the time is in minutes not hours.

animesh mohanty · Answer

change of 5 mph =0.083 miles per min which is achieved in 30 mins. This is the same as change of 0.041 miles per min that is achived in 15 mins. so the logic is correct.
P.S. i didn't mark the difference initially. Thank!

sonamme109 · Answer

calculate the speed by substituting time at t= 30 minutes.
t= 30 minutes = 1/2 hrs
E- 40+10t = 40+10*1/2 = 40+5 = 45 mph

hence E is the answer.

generis · Answer

I think elimination might be quicker. Find one pair of correlated numbers (time, speed), to disprove each answer. I varied it just to be careful.

(A) t/6? S = 45, t = 30 
45 
eq (30/6) = 5: NO

(B) 10t? S = 50, t = 60
50  
eq (10 * 60) = 600: NO

(C) 40 + t? S = 55,t = 90
55  
eq  (40 + 90) = 130: NO

(D) 40 + t/6? S = 60, t = 120
60 = (40 + 120/6) = (40 + 20) = 60
First test works. Come back

(E) 40 + 10t? S = 70, t = 180
70  
eq (40 + 180) = 220: NO

By POE, D is the answer. Test it: 
50 S, 60t: (40 + 60/6) = (40 + 10) = 50
45 S, 30t: (40 + 30/6) = (40 + 5) = 45

That's enough.

Answer D

pavanm26 · Answer

time is given in minutes and speed in m.p.h
60 min = 1 hr
 in the table 60 min gives speed as 55
Answer E satisfies the condition
40 + 10(1) = 50

validation: for 90 min: t = 3/2
40 + 10(3/2)= 55

JeffTargetTestPrep · Answer

Let’s plug in values from the table. In the first column, we have t = 0 for time and speed = 40.

We see that C, D, and E yield a speed of 40 when using 0 for t.

Testing the second column, we have t = 30 and speed = 45. Thus, we see that answers C and E do not yield 45 when t = 30. Answer choice D yields 40 + 30/6 = 45.

Answer: D

samriddhi1234 · Answer

Hi  JeffTargetTestPrep

In line with some of the answers above that ave given the answer E, which is what I got as well - why are we taking the value of speed as it is, when it has a different unit compared to time? why aren't we converting it?

would really appreciate if you could throw more light here. thank you!

RBgmatPre · Answer

I had similar doubt as yours

One possible explanation of this could be -

The options given are a formula - A formula that is designed to take input of 't' in minutes and give the output in miles per hour

harjas2222 · Answer

i did not understood the question, can anyone explain?

At time t measured in minutes after the beginning of the timed period,

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

At time t measured in minutes after the beginning of the timed period,

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards