Park leaves home for work and drives at 30mph. 20 mins later Susan realizes he left his tool box at home. If she drives at 40 mph,?

how far she drives before she overtakes him? Correct answer is 40. Can somebody please explain how to get to the answer?

2 Answers

  • 6 years ago
    Favorite Answer

    Assuming they took the same route:

    x hours after Susan leaves, she has driven 40x miles

    Since Park left 20 minutes earlier, that's 1/3 of an hour earlier, so he has driven for x + (1/3) hours, so he has driven 30(x + (1/3)) = 30x + 10 miles.

    When they meet:

    40x = 30x + 10

    40x - 30x = 10

    10x = 10

    x = 10/10

    x = 1

    So Susan has driven for 1 hour, so she drove 40*1 = 40 miles.

  • David
    Lv 7
    6 years ago

    In 20 minutes, Park will have gone 10 miles. There is a 10 miles per hour differential in speed. That means every four minutes, Susan catches up 1 mile. To overtake the 10 mile advantage, take 4x10. QED

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