This question was previously asked in

IBPS RRB Officer Scale - 1 August 2021 Shift 1 Memory Based Test

Option 2 : 5 days

**Given:**

Time taken to complete the work by A = 12 days

Time taken to complete the work by B = 20 days

Time taken to complete the work by C = 15 days

A and B started the work and worked for 5 days

**Concept used:**

Efficiency = Total work / Time

**Calculation:**

LCM of 12, 20 and 15 = 60 units = Total work

Efficiency of A = 60/12

⇒ 5 units/days

Efficiency of B = 60/20

⇒ 3 units/days

Efficiency of C = 60/15

⇒ 4 units/days

Total work done by A and B together in 5 days = (5 + 3) × 5 units

⇒ 40 units

Remaining work = (60 – 40) units

⇒ 20 units

Time taken by C to complete the remaining work = 20/4 days

⇒ 5 days

**∴ C will complete the remaining work in 5 days**