A can do a piece of work in 18 days. B can do this work in 24 days. A started the work alone. After how many days should B join him, so that the work is finished in 15 days?

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SSC GD Constable (2022) Official Paper (Held On : 01 Feb 2023 Shift 3)
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  1. 11 days
  2. 19 days
  3. 13 days
  4. 14 days

Answer (Detailed Solution Below)

Option 1 : 11 days
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Detailed Solution

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Given:

A can do a piece of work in 18 days,

B can do the same work in 24 days,

Work is finished in 15 days

Concept:

Work done = Time × Work rate

Calculation:

Let the total work = LCM(18, 24) = 72 units

So,

Efficiency of A = 72/18 = 4 units

Efficiency of B = 72/24 = 3 units

A starts the work, so A works for 15 days.

So,

Work completed by A = 15 × 4 = 60 units

So,

Work completed by B = 72 - 60 = 12 units

So,

B works for = 12/3 = 4 days

So,

B joins the work after = 15 - 4 = 11 days

Therefore, B should join A after 11 days.

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