On a lengthy north-south highway, points X and Y are situated such that Y is 420 km south of X. A vehicle departs from X while another leaves from Y simultaneously. If they drive towards each other, they will intersect after 1 hour. Conversely, if both head towards the north, they will converge in 6 hours. What is the difference between their speeds, in km per hour?

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Official Explanation

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Let the speeds of the vehicles be v and u. Then, we have the equations v + u = 420 (from their meeting after 1 hour) and v - u = 420/6 = 70 (from their…

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Comments

SaiSep 21, 2024

this pattern comes up frequently

MuditMar 27, 2024

Great

What this question tests

What it tests

Your application of distance = rate × time to trains, boats, and commuters, including relative speed.

Common trap

Mixing units (miles per hour vs. minutes) or averaging speeds — average speed is total distance over total time.