Multiple choice

David and Michael together can finish a job in4 days 19 hrs 12 min. If David works at twothirds Michael's speed, how long does it takeMichael alone to finish the same job?

  1. 12DAYS

  2. 15DAYS

  3. 8DAYS

  4. 17DAYS

  5. 11DAYS
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let M be Michael's rate. David's rate = 2/3 M. Combined rate = 5/3 M. Total time = 4 days 19 hrs 12 min = 115.2 hours. Total work = (5/3 M) * 115.2 = 192 M. Michael alone takes 192/M = 192 hours = 8 days.

AI explanation

Convert the combined time to 4.8 days, and let Michael's speed be 3x, which makes David's speed 2x. Their combined speed is 5x, so using the formula (Speed) * (Time) = (Work), the total work is 5x * 4.8 = 24x units. Michael alone works at 3x units per day, so the time he takes is 24x / 3x = 8 days.

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