Ravi and Raju can do a piece of work separately in 12 days and 20 days, respectively. If they work alternate days, with Ravi starting first, then in how many days will they complete the entire work?

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  1. 14.3
  2. 15.4
  3. 14.8
  4. 15.2

Answer (Detailed Solution Below)

Option 3 : 14.8
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Detailed Solution

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Given:

Time taken by Ravi = 12 days

Time taken by Raju = 20 days

Ravi starts first, working on alternate days.

Formula Used:

Total Work = LCM of time taken by individuals

Efficiency = Total Work / Time taken

Calculation:

Total Work = LCM(12, 20) = 60 units

Efficiency of Ravi = Total Work / Time taken by Ravi = 60 / 12 = 5 units/day

Efficiency of Raju = Total Work / Time taken by Raju = 60 / 20 = 3 units/day

Work done in the first 2 days (Ravi then Raju) = Efficiency of Ravi + Efficiency of Raju = 5 + 3 = 8 units

Number of 2-day cycles to complete most of the work = Total Work / Work done in 2 days ≈ 60 / 8 = 7.5 cycles

Work done in 7 cycles (14 days) = 7 × 8 = 56 units

Remaining work = Total Work - Work done in 14 days = 60 - 56 = 4 units

On the 15th day, it's Ravi's turn. Ravi can do 5 units of work in a day.

Since only 4 units of work are remaining,

Time taken by Ravi to complete it = 4/5 days

Total days taken = 14 (for 7 cycles) + 4/5 (on the 15th day by Ravi) = 14.8 days.

They will complete the entire work in 14.8 days.

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