Mrs.Robbins started half an hour later than usual for market

Question

Mrs. Robbins started half an hour later than usual for market. But by increasing her speed to 3/2 times her usual speed she reached 10 mins earlier than usual. What is her usual time for this journey?

A. 2 hrs
B. 1 hr
C. 43 MINS
D. 1,5 hrs

KarishmaB · Accepted Answer

Since she covers the same distance, if she increases her speed by 3/2, the time taken by her becomes 2/3 of her usual time. (When distance is constant, speed will be inversely proportional to time.)

The 1/3rd difference in time taken in 30 mins + 10 mins = 40 mins. then her usual time must be 40 * 3 = 120 mins = 2 hrs.

Bunuel · Answer

Let the usual speed be s and usual time t minutes, then as the distance covered is the same we will have: st=1.5s*(t-30-10) --> t=120 minutes (2 hours). Answer: A. Similar questions to practice: each-day-a-man-meets-his-wife-at-the-train-station-after-93545.html a-man-arrives-at-a-railway-station-90mins-before-the-time-at-100073.html ray-who-lives-in-the-countryside-caught-a-train-for-home-ea-84295.html two-guns-were-fired-from-the-same-place-at-an-interval-of-93761.html Hope it helps.

WholeLottaLove · Answer

Mrs. Robbins started half an hour later than usual for market. But by increasing her speed to 3/2 times her usual speed she reached 10 mins earlier than usual. What is her usual time for this journey?

s=original speed
t=original time

I always have had difficulty setting up these types of problems; rate, work, time, etc. This one is no different! We are looking to set the original time and speed to a new, lesser time and greater speed. In effect, the smaller value for the time multiplied by the greater speed balances it out, correct?

s*t = 1.5s*(t-30-10) 
 When she starts off 30 minutes late and arrives 10 minutes early, she effectively spends 30 minutes less time on the road (because she set off late) and another 10 minutes less because she got there early. In effect, she shaves 40 minutes off her normal time spent driving. 
st = 1.5s*(t-40)
st = 1.5st-60s
t = 1.5t-60
-.5t=-60
t=120

ANSWER: A. 2 hrs

PareshGmat · Answer

This question does not have the 5th option?

Usual Speed = s

Usual Time = t

When Late

Time = t - 30 - 10 = t-40 (For 30 minutes, she was idle at home; for 10 Minutes, she was idle at station)

Speed  = \frac{3s}{2}

st = \frac{3s}{2} (t-40)

t = 120 Minutes

Answer = A

KarishmaB · Answer

This is not a GMAT question so its format doesn't align, but it is based on the fundamentals tested in GMAT.

mvictor · Answer

i tried to plug in numbers, but forgot about the 30 minutes delay...
if t=2, then D = 2r.
then we have new rate 1.5r, and distance is 2r. so 2r/1.5r = 4/3, or 80 minutes. since we have 30 minutes delay, total - 110 minutes. 10 minutes earlier than regular. A works and don't even need to test other numbers.

gracie · Answer

let r=usual rate
let t=usual time
rt=(3r/2)(t-2/3)
t=2 hours

shaktirdas19 · Answer

Mrs.Robbins started half an hour later than usual for market. But by increasing her speed to 3/2 times her usual speed she reached 10 mins earlier than usual. What is her usual time for this journey?

A) 2 hrs
B)1 hr
C)43 MINS
D)1,5 hrs

Let distance covered by Mrs.Robbins is D,speed is S,usual time is T.
D=ST----1
New speed is (3/2)S.
New time is T-(30/60)-(10/60) as she starts 30 mins late and reaches 10 mins early.
As distance covered is same so :D/((3/2)S)=T-(30/60)-(10/60)----2.
Solving 2 and substituting 1 in 2 we get T=2hours or 120 mins.
Ans:A

vituutiv · Answer

Can anyone spot what's wrong with my reasoning? I couldn't

Time to walk D x km/h: T Time to walk D @ 3/2 x: 2/2 T She arrived 1/6 h earlier, thus total time was 5/6 T (Time taken) = (Time stopped) + (Time to walk D) 5/6 T h = 0,5 h + 2/3 T T = 3 h I can't find the flaw!

Klarbeinstreiter · Answer

vituutiv I think the problem comes from two parts 1) You assume that T=1h but that information is not provided. If we'd knew T we'd have the answer directly 8-)

Time to walk D x km/h: T Time to walk D @ 3/2 x: 2/ 2 3 T She arrived 1/6 h earlier, thus total time was 5/6 T ->That means 10 minutes = 1/6T for you and subsequently 0,5h = 3/6T (Time taken) = (Time stopped) + (Time to walk D) 5/6 T h = 0,5 h 3/6T + 2/3 T // That would mean: 5/6 T=3/6 T+4/6 T = 7/6 T T = 3 h 2) The question asks for her usual travel time not the time she needed on this day Therefore you are looking probably for something like this: 3/3T (her normal travel time) = 2/3T (time to walk D) + 40 (the time she needs less ) => 1/3T = 40 => T= 120

vituutiv · Answer

Oh, that's exactly it. Such a silly mistake.

Thank you very much for the help!

Turkish · Answer

Hello Bunnel,

I am just failing to understand this. I am sure this is a silly one.

When the question says "started half an hour later than usual" so she usually starts @9am now she will start @ 9.30. Shouldn't it be t+30 and then " she reached 10 mins earlier" so t+30-10 mins. or t+20 ?

ScottTargetTestPrep · Answer

We can let Mrs. Robbins’ regular speed = r and her distance = d. Thus, her increased rate is 3r/2. Her regular time is d/r, and so her new time will be d/(3r/2) = 2d/3r. Since she started ½ hour, or 30 minutes, late but arrived at the market 10 minutes early, her new time is 40 minutes shorter than her old time and we have:

2d/3r + 40 = d/r

Multiplying by 3r, we have:

2d + 120r = 3d

120r = d

120 = d/r

Since d/r = her old time, her old time must be 120 minutes, or 2 hours.

Answer: A

testtakerstrategy · Answer

Bunuel , what is the standardized way to solve this? I am not sure how to approach this systematically

Kinshook · Answer

Given: Mrs. Robbins started half an hour later than usual for market. But by increasing her speed to 3/2 times her usual speed she reached 10 mins earlier than usual.

Asked: What is her usual time for this journey?

Let her usual time for the journey be t hrs and speed be v kmh.

D = vt = 3v/2 (t-.5 - 10/60) = 1.5vt - .75v - .25v = 1.5vt - v
.5vt = v
t = 2 hrs

IMO A

bumpbot · Answer

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.

Mrs.Robbins started half an hour later than usual for market

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

Mrs.Robbins started half an hour later than usual for market

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