Multiple choice

A can do a certain piece of work in the same time in which B and C together can do it. If A and B together could do it in 15 days and C alone in 40 days . then B alone could do the same work in how many days? A किसी काम को जितने समय में करता है उतने ही समय में B व C भी साथ मिलकर करते है A तथा B किसी कार्य को 15 दिन में करते है और C अकेला 40 दिनों में करता है तो B अकेला कितने दिनों में काम समाप्त करेगा ?

  1. 24

  2. 36

  3. 42

  4. 48
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let A, B, C take a, b, c days respectively. A = B + C combined work, so 1/a = 1/b + 1/c. A + B together: 1/a + 1/b = 1/15. C alone: 1/c = 1/40. Substituting: 1/a + 1/b = 1/15 and 1/a = 1/b + 1/40. From second: 1/a - 1/b = 1/40. Adding with first: 2/a = 1/15 + 1/40 = 11/120, so a = 240/11. Then 1/b = 1/15 - 11/240 = 5/240 = 1/48, so b = 48 days.

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