Supraja and Kausalya can complete a work in 30 days and 20 days, respectively. If Supraja starts the work and they work on alternate days, in how many days will 75% of the work be completed?

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SSC CGL 2023 Tier-I Official Paper (Held On: 20 Jul 2023 Shift 3)
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  1. 28
  2. 24
  3. 20
  4. 18

Answer (Detailed Solution Below)

Option 4 : 18
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Detailed Solution

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Given: 

Supraja and Kausalya can complete a work in 30 days and 20 days, respectively.

Supraja starts the work and they work on alternate days.

Concept used:

Efficiency = (Total work / Total time taken)

Efficiency = work done in a single day 

Calculation:

Let the total work is the 60 units (LCM of 30 and 20)

The efficiency of Supraja is 60 / 30 = 2 units

The efficiency of Kausalya is  60 / 20 = 3 units

In 2 days they do 3 + 2 = 5 units

75% of the total work is 60 × 3/4 = 45 units

So they will take (45 / 5) × 2 = 18 days.

∴ The correct option is 4

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