A contractor estimates that 3 persons could rewire Jasminder's house in 4 days. If he uses 4 persons instead of three, how long should they take to complete the job?

According to the estimation in rewiring Jasminder's house
Number of persons required = 3
Number of days required = 4
So, to rewire a house by 1 person it will take 4 × 3 = 12 days
And to do the job by 4 persons, days required = 12 / 4 = 3 days