A ball is dropped from a height of 10 m. It strikes the ground and rebounds up to a height of 2. m. During the collision, the per cent loss in the kinetic energy is
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?