GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

It is currently 03 Apr 2020, 15:26

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Find Similar Topics 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 62496
If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.  [#permalink]

Show Tags

New post 04 Feb 2020, 09:22
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

65% (02:22) correct 35% (01:48) wrong based on 59 sessions

HideShow timer Statistics

If Robin drives at 20 kilometer per hour, she reaches office at 3 pm. If she drives at 30 kilometer per hour, she reaches office at 11 am. At what speed she should drive if she wishes to reach office at 1 pm ?

A. 23 kilometer per hour
B. 24 kilometer per hour
C. 25 kilometer per hour
D. 26 kilometer per hour
E. 27 kilometer per hour

_________________
Director
Director
avatar
P
Joined: 25 Jul 2018
Posts: 628
If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.  [#permalink]

Show Tags

New post 04 Feb 2020, 09:40
1
Using the formula:
—> Speed* Time = Distance
If she comes at 3:00 p.m, then
—> 20 *T = D
If she comes at 11:00 a.m, then
—> 30*(T—4)= D

30*T —120 = D
20*T = D
—> 10T = 120 —> T = 12
D = 12*20 = 240

If she wishes to come at 01:00 p.m, then —> speed *(12–2) = 240
—> Speed = 240/10 = 24 kilometer per hour

The answer is B

Posted from my mobile device
Senior Manager
Senior Manager
User avatar
P
Status: So far only Dreams i have!!
Joined: 05 Jan 2015
Posts: 285
WE: Consulting (Consulting)
Premium Member Reviews Badge
Re: If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.  [#permalink]

Show Tags

New post 04 Feb 2020, 09:46
Given:
- Robin drives at 20 kilometer per hour, she reaches office at 3 pm.
- If she drives at 30 kilometer per hour, she reaches office at 11 am

- Increase in speed = 1/3(of 20kmph) as speed becomes 2/3rd (30kmph)
- Since time is inversely proportional, equivalent decrease 1/3(Total time) = 4 hrs
- We get total time taken = 12 hrs

- distance = 12*20 = 240 kms
- To reach at 1 pm(in 10 hrs), 240/10 = 24kmph

IMO Option B
_________________
Unable to Give Up!
Intern
Intern
avatar
B
Joined: 14 Aug 2017
Posts: 26
GMAT ToolKit User
Re: If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.  [#permalink]

Show Tags

New post 05 Feb 2020, 19:00
Hi,
I have taken the following approach to solve this question. Please correct me if I am wrong.

Let us assume that t is the time at which Robin Starts.
Let d be the total distance.
Since we don't know the exact time at which Robin Started, we will have to find out the starting time t.
We will consider all the time in 24 hours time, so that we can calculate the time taken in hours by Robin to reach the office by calculating the difference between the time Robin reaches the office and time when she starts(t) and equating it in the speed-time-distance- formula.

so in 24 hours time zone, 3:00 pm => 15:00

Now we will have to use the speed-time-distance-formula
Distance = Speed * Time
substituting the values,
\(d=(15-t)*20\) .....(i) => this is the case when Robin travels at a speed of 20km/h and reaches office at 3pm(15:00 in 24 hours time zone)
\(d=(11-t)*30\) .....(ii) => this is the case when Robin travels at a speed of 30km/h and reaches office at 11 am(11:00 in 24 hours time zone)

From equations (i) and (ii), we get,
\(20*(15-t)=30*(11-t)
300-20t=330-30t
10t=30
t=3
\)
\(d = (11-3)*30=240\)

Now let s be the speed at which Robin has to travel to reach office at 1:00 pm(13:00 24 hours).

We will again use the speed-time-distance-formula,

\(d = s*t\)

on substituting the values, we get,
\(240=s*(13-3)
240=s*10
s=24\)

so option B, 24km/h is the correct answer.
Veritas Prep GMAT Instructor
User avatar
V
Joined: 16 Oct 2010
Posts: 10240
Location: Pune, India
Re: If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.  [#permalink]

Show Tags

New post 05 Feb 2020, 20:30
1
Bunuel wrote:
If Robin drives at 20 kilometer per hour, she reaches office at 3 pm. If she drives at 30 kilometer per hour, she reaches office at 11 am. At what speed she should drive if she wishes to reach office at 1 pm ?

A. 23 kilometer per hour
B. 24 kilometer per hour
C. 25 kilometer per hour
D. 26 kilometer per hour
E. 27 kilometer per hour


Use Ratios:

Ratio of speeds = 20:30
Ratio of time taken = 3:2 (inversely proportional)
The difference of 1 in time taken is actually equal to 4 hrs (3pm - 11 am). So actual time taken in the two cases is 12 hrs and 8 hrs.

If time taken needs to be 10 hrs, ratio of time taken = 12:10 = 6:5 (in case of 20km/hr and New case)
Ratio of speeds = 5 : 6 = 20 : S
S = 24 km/hr

Answer (B)
_________________
Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
Manager
Manager
avatar
B
Joined: 14 Sep 2019
Posts: 220
Re: If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.  [#permalink]

Show Tags

New post 06 Feb 2020, 00:14
Let the distance = x km

x/20 – x/30 = 4(Distance/ Rate = Time and Difference between 11 am and 3 pm is equal to 4 hours)

3x – 2x/60 = 4
x/60 = 4
x = 240

When he reaches at 3 pm, he will take time = 240/20 = 12 hours

If he wants to reach
Now , rate * time = Distance
R = 240/10(As he wants to reach at 1 pm, he will take 10 hours)
R = 24 km/hour


Answer:24 km/hour(B)
Target Test Prep Representative
User avatar
V
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 9952
Location: United States (CA)
Re: If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.  [#permalink]

Show Tags

New post 08 Feb 2020, 19:10
Bunuel wrote:
If Robin drives at 20 kilometer per hour, she reaches office at 3 pm. If she drives at 30 kilometer per hour, she reaches office at 11 am. At what speed she should drive if she wishes to reach office at 1 pm ?

A. 23 kilometer per hour
B. 24 kilometer per hour
C. 25 kilometer per hour
D. 26 kilometer per hour
E. 27 kilometer per hour


Let t = the number of hours she should drive in order to reach her office at 1 pm. We can create the equation:

20(t + 2) = 30(t - 2)

20t + 40 = 30t - 60

100 = 10t

10 = t

Thus, the distance is 20 x 12 = 240 (or 30 x 8 = 240) km.

So, if Robin wants to arrive at 1 pm, she should drive at 240/10 = 24 kmph.

Answer: B
_________________

Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
TTP - Target Test Prep Logo
197 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

GMAT Club Bot
Re: If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.   [#permalink] 08 Feb 2020, 19:10
Display posts from previous: Sort by

If Robin drives at 20 kilometer per hour, she reaches office at 3 pm.

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  





cron

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne