Lesson: Introduction to GMAT Motion Questions

Comment on Introduction to GMAT Motion Questions

The easy questions in the example are much harder than the examples from the ones you did in the video. The explanations in the example question links aren't that clear. Do you have any other lessons to solve more complex problems for this topic?

Thanks
gmat-admin's picture

This first lesson serves as an introduction to motion problems. In total, there are 4 videos lessons on motion questions. So, if you're having difficulties with the linked questions above, you might want to watch all 4 lessons first and then return to these questions.

Awesome thanks

can we solve this question (https://gmatclub.com/forum/teneka-and-francis-leave-town-a-at-9-00-a-m-driving-north-along-highw-239035.html) using the shrinking rate of 10 m/h ?
gmat-admin's picture

Question link: https://gmatclub.com/forum/teneka-and-francis-leave-town-a-at-9-00-a-m-d...

Actually, 10 mph is the EXPANSION rate (not the shrink rate). Since they both start at the same point, and since Francis is traveling 40 mph and Teneka is traveling 30 mph, their distance apart EXPANDS by 10 miles every hour.

However, once Francis' car breaks down and stops, the shrink rate is no longer 10 mph. At this point, Francis' speed is 0 mph and Teneka's speed is 30 mph. At this point, their distance apart SHRINKS at a rate of 30 miles each hour.

Does that help?

Cheers,
Brent

right expansion rate. i called it shrinking, because once the car stopped, the gap is shrinking, not expanding. but now i understand your point of shrinking vs expanding.

my problem is that the question looked perfect for going the shrinking or expansion route since it provided two speeds. it is kind a confusing to differentiate when i should approach a problem using the expanding/shrinking approach vs not using it.

thanks.
gmat-admin's picture

We can definitely use the strategies for shrinking and expanding gaps.

For the first 240 miles of Francis's trip, we have an expansion scenario (where the expansion rate = 10 mph)

Once Francis' car breaks down and stops, we have a shrinking scenario (where the gap shrinks at a rate of 30 mph)

Does that help?

Cheers,
Brent

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