31 men can complete half of the work in 21 days. Find the number of days in which 7 men can complete the remaining work.

Some useful tips for solving Time & Work problems are: 1. Work Done = Time Taken × Rate of Work 2. Rate of Work = 1 / Time Taken 3. Time Taken = 1 / Rate of Work 4. If a piece of work is done in x number of days, then the work done in one day = 1/x 5. Total Wok Done = Number of Days × Efficiency 6. Efficiency and Time are inversely proportional to each other 7. X:y is the ratio of the number of men which are required to complete a piece of work, then the ratio of the time taken by them to complete the work will be y:x 8. If x number of people can do W1 work, in D1 days, working T1... Show more

Some useful tips for solving Time & Work problems are:

1. Work Done = Time Taken × Rate of Work
2. Rate of Work = 1 / Time Taken
3. Time Taken = 1 / Rate of Work
4. If a piece of work is done in x number of days, then the work done in one day = 1/x
5. Total Wok Done = Number of Days × Efficiency
6. Efficiency and Time are inversely proportional to each other
7. X:y is the ratio of the number of men which are required to complete a piece of work, then the ratio of the time taken by them to complete the work will be y:x
8. If x number of people can do W1 work, in D1 days, working T1 hours each day and the number of people can do W2 work, in D2 days, working T2 hours each day, then the relation between them will be: 

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