19. A sum of money is sufficient to pay A�s wages for 21 days or B�s wages for 28 days. The money is sufficient to pay the wages of both for:

20. A, B and C contract a work for Rs. 550. Together A and B are to do of the work. The share of C should be:

21. A and B can together finish a work in 30 days. They worked for it for 20 days and then B left. The remaining work was done by A alone in 20 more days. A alone can finish the work in: