Multiple choice

If A takes half as long to do a piece of work as B takes, and if C takes the time same as A and B together, and if all three, working together take 7 days, then how long would each take separately?

  1. 21 days, 21 days, 14 days

  2. 21 days, 42 days, 14 days

  3. 21 days, 21 days, 21 days

  4. 7 days, 14 days, 28 days
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let A's rate be 2x, B's rate be x, and C's rate be 3x. Combined rate is 6x. Since they take 7 days together, 6x * 7 = 1 (total work), so x = 1/42. A takes 21 days, B takes 42 days, and C takes 14 days.

AI explanation

Let B's time to complete the work be x days; then A takes x/2 days, and their combined rate is 2/x plus 1/x, which equals 3/x. Since C takes the same time as A and B together, C's rate is also 3/x, making the combined rate of all three equal to 6/x. Setting 6/x equal to 1/7 of the work per day gives x equals 42, meaning B takes 42 days, A takes 21 days, and C takes 14 days.

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