Question

4 man and 5 boys can do a piece of work in 20 days which 5 man and 4 boys can do the same work in 16 days .In how many days

Answer 1

4 days is the right answer

Answer 2

See this is a time and work question which means a relationship will be established which is opposite to the simple UP-UP relationship, where when the variables increase the cost increases. Here on the other end, when more men do the work, it is done is less time, establishing a UP-DOWN relationship....
Let man by boy be x and by man be y and solve it