Robin and Varun together can paint a hall in 6 days. Robin alone can paint it in 42 days. In how many days can Varun alone paint it?

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RRB NTPC Graduate Level CBT-I Official Paper (Held On: 05 Jun, 2025 Shift 3)
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  1. 7
  2. 9
  3. 10
  4. 8

Answer (Detailed Solution Below)

Option 1 : 7
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RRB NTPC Graduate Level Full Test - 01
100 Qs. 100 Marks 90 Mins

Detailed Solution

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Given:

Robin and Varun together can paint in 6 days

Robin alone can paint in 42 days

Formula used:

Work = LCM of days taken

Efficiency = Work ÷ Time

Time taken by Varun = Total work ÷ Varun’s efficiency

Calculations:

⇒ LCM of 6 and 42 = 42

⇒ Total work = 42 units

⇒ Robin’s 1 day work = 42 ÷ 42 = 1 unit

⇒ Together 1 day work = 42 ÷ 6 = 7 units

⇒ Varun’s 1 day work = 7 - 1 = 6 units

⇒ Time = 42 ÷ 6 = 7 days

∴ Varun alone can paint the hall in 7 days.

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