Shrinking and Expanding Gaps for GMAT questions

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Question link: https:/

gmat-admin - March 3, 2020

Question link: https://gmatclub.com/forum/mary-and-kate-are-running-clockwise-around-a-...

The question asks "If Mary and Kate start opposite one another on the circular track,...."

In my opinion, this is a perfectly valid way to phrase the question.

Cheers,
Brent

Great video. Quick question:

How do you know when to add the rates and when to subtract the rates? I'm looking in one of the ManhattanPrep books and it says to add the rates when objects move towards each other. The rates were subtracted in the BeatTheGMAT problem below.

Thanks.

https://gmatclub.com/forum/a-gang-of-criminals-hijacked-a-train-heading-due-south-239444.html

Question link: https:/

gmat-admin - April 12, 2020

Question link: https://gmatclub.com/forum/a-gang-of-criminals-hijacked-a-train-heading-...

Great question!
There are three different cases to consider.

Case i: two cars are driving towards each other
In this case, we have a shrinking gap situation, and the rate at which the gap shrinks equals the SUM of the two speeds.

Case ii: two cars are driving away from each other
In this case, we have an expanding gap situation, and the rate at which the gap expands equals the SUM of the two speeds.

Case iii: two cars are driving in the same direction
In this case, depending on the situation, the gap will either be shrinking or expanding.
The rate at which the gap expands or shrinks equals the DIFFERENCE between the two speeds.

Does that help?

Cheers,
Brent

Stations X and Y are

Aripiakshaya - April 29, 2020

Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination?

(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour.
(2) Train Q averaged a speed of 55 miles per hour for the entire trip.
I could not understand your explanation for statement 2 and on what basis you have taken the total time of p is 4 hrs. I am confused. Pls make me understand

Link to my solution: https:/

gmat-admin - April 29, 2020

Link to my solution: https://gmatclub.com/forum/stations-x-and-y-are-connected-by-two-separat...

My bad. I've now fixed my solution.
I intended to make Train P's travel time 4.5 hours (so that it's the same as Train Q's travel time).
Keep in mind that we aren't provided any information about Train Q's travel time; it was just easier for me to show 2 contradictory cases if I made both travel times 4.5 hours.

Does that help?

Hi Brent,

Aripiakshaya - May 1, 2020

Hi Brent,
Pls explain this
Yesterday, Candice and Sabrina trained for a bicycle race by riding around an oval track. They both began riding at the same time from the track's starting point. However, Candice rode at a faster pace than Sabrina, completing each lap around the track in 42 seconds, while Sabrina completed each lap around the track in 46 seconds. How many laps around the track had Candice completed the next time that Candice and Sabrina were together at the starting point?

A. 21
B. 23
C. 42
D. 46
E. 483

Here's my full solution:

gmat-admin - May 1, 2020

Here's my full solution: https://gmatclub.com/forum/yesterday-candice-and-sabrina-trained-for-a-b...

Cheers,
Brent

Hi Brent, Could you please

Joelle2020 - May 5, 2020

Hi Brent, Could you please help on this one ? thank you

Jayvee and Varun stand back-to-back.They each take 20 steps in opposite directions away from each other and stop. Jayvee turns around, walks towards Varun, and reaches him in 30 steps. If all of Jayvee's steps are of same length and also all of Varun's steps are of the same length, the length of one of Jayvee's steps is how many times the length of one of Varun's steps ?
A:1, B:2, C:5, D:10, E:2,5

Let J = length of ONE Jayvee

gmat-admin - May 5, 2020

Let J = length of ONE Jayvee step
Let V = length of ONE Varun step

So, after 20 steps, Jayvee's distance = 20J
And after 20 steps, Varun's distance = 20V

So, after they both take 20 steps, the total distance between them = 20J + 20V

Once Jayvee turns around, he's able to cover the entire distance in 30 steps.
In 30 steps, Jayvee's distance = 30J

So, we can write: 20J + 20V = 30J
Subtract 20V from both sides to get: 20V = 10J
Divide both sides by 10 to get: 2V = J
In other words, Jayvee's step distance = 2(Varun's step distance_

Answer: B

Cheers,
Brent

https://gmatclub.com/forum

Kashaf Mushahid - September 4, 2020

https://gmatclub.com/forum/jerry-and-jim-run-a-race-of-2000-m-first-jerry-gives-jim-122757.html

Hi Brent, is this an official GMAT Question? This seems to be really tough and lengthy to solve in 2 minutes.

Yes, it's an official GMAT

gmat-admin - September 4, 2020

Yes, it's an official GMAT question.
Keep in mind that the question has a 95% difficulty rating (the highest rating a question can have) on GMAT Club. So it's definitely a 700+ level question.

By the way, here's my solution: https://gmatclub.com/forum/jerry-and-jim-run-a-race-of-2000-m-first-jerr...

These questions are very hard

sjiang24 - October 14, 2021

These questions are very hard for me...I literally got nothing correct, what should I do..

A lot of students struggle

gmat-admin - October 15, 2021

A lot of students struggle with this question type.
You might start by re-watching the video lesson. Also, be sure to review various solutions (by experts) to the linked questions in the Reinforcement Activities box.
After all of that, here are a few more questions to practice with:

- https://gmatclub.com/forum/oscar-is-running-in-a-straight-line-away-from...

- https://gmatclub.com/forum/a-policeman-is-running-after-a-thief-who-has-...

- https://gmatclub.com/forum/two-people-start-jogging-at-the-same-point-an...

- https://gmatclub.com/forum/two-cars-are-traveling-in-the-same-direction-...

- https://gmatclub.com/forum/trains-a-and-b-start-simultaneously-from-stat...

- https://gmatclub.com/forum/one-hour-after-adrienne-started-walking-the-6...