Amit is 70% more efficient than Ajay, ⇒ Efficiency Ratio of Ajay and Amit = 10 ∶ 17 ⇒ Ratio of no. of days of Ajay and Amit = 17 ∶ 10 [∵ Efficiency and days are inversely proportional to each other] Ajay can do a painting in 12 days, ⇒ 17 units = 12 ⇒ 10 units = 12 × 10/17 = 120/17 ∴ Amit would need 7