The average salary of all the workers in a workshop is Rs. 8000. The average salary of 7 technicians is Rs. 12000 and the average salary of the rest is Rs. 6000. The total number of workers in the workshop is

A trader's marked price is 30% above the cost price and gives 1 articles free for buying every 15 articles and thus gains 35%. The marked price in increased above the cost price by

A can do a piece of work in 60 days. He worker for 15 days and then B alone finishes the remaining work in 30 days. The two together can finish the work in