Correct Answer - Option 2 : 10 days

**Given:**

Days taken to built a house = 80 days

Men worked for first 70 days = 100

Men worked after 70 days = 200

**Formula Used:**

Men_{1} × Efficiency_{1} × Days_{1}/Work_{1} = Men2 × Efficiency2 × Days_{2}/Work2

**Calculation:**

After 70 days

The remaining work completed by 200 men in 10 days

⇒ 100 men will complete this work in

⇒ 200/100 × 10 = 20 days

⇒ The delay in work

⇒ (70 + 20) - 80 = 10 days

**∴ If he didn't hire extra workers there will be delay of 10 days.**