Two workers, Ravi and Suresh, started a project together. They worked together for the first 5 days, but only 25% of the project was completed. So, Ravi and Suresh increased their respective efficiencies by 50% each, such that the work was completed on time. If they had not increased their respective efficiencies, then the work would have been delayed by how many days?

Let, efficiencies of Ravi and Suresh be 'x' units/day and 'y' units/day, respectively So, total work = (5x + 5y) × 4 = (20x + 20y) units Work done in first 5 days = (5x + 5y) units Remaining work = 20x + 20y – 5x – 5y = (15x + 15y) units Increased efficiencies of Ravi and Suresh are 1.5x units/day and 1.5y units/day, respectively. So, '15x + 15y' units of work will be done in (15x + 15y)/(1.5x + 1.5y) = 10 days Total time taken to complete the work = 5 + 10 = 15 days And, if efficiencies were not increased then total work will be done in (20x + 20y)/(x + y) = 20 days Required number of days = 20 – 15 = 5 days