Option 2 : 50

NTPC Diploma Trainee 2020: Full Mock Test

12144

120 Questions
120 Marks
120 Mins

**Given:**

Efficiency ratio of grandfather, father, mother and son is 3 ∶ 4 ∶ 2 ∶ 1.

**Concept used:**

Let the ration given be their actual efficiency like grandfather's is 3 units per day.

**Formula used:**

Total work = efficiency × time

Time taken = (total work)/(efficiency)

Similarly,

father's efficiency is 4 units per day.

mother's efficiency is 2 units per day.

son's efficiency is 1 unit per day.

**Calculations:**

Total work = 10 units × 10 days

⇒ 100 units

Time taken by grandfather & son to complete the double work = (2 × 100 units)/(3 + 1) units

⇒ 50 days

**∴ Time taken by grandfather & son to complete the double work is 50 days**