A and B together can finish a work in 30 days. They worked for it for 20 days and then B left the work. The remaining work was done by A alone in 20 days more. In how many days can A alone finish the work?
A ceramic pottery unit hires 8 craftsmen by paying each of them Rs 900 per day. The 9th craftsman demands Rs 950 per day. If this craftsman is hired then all other craftsmen must be paid Rs 950. The marginal resource (labour) cost of the 9th craftsman is _________.