An ant farm contains both red and black ants. A particular passage in the farm is so narrow that only 1 ant can get through at a time. If 10 ants (5 red and 5 black) follow each other through the passage, how many different colour patterns can be produced (assuming that the red ants are indistinguishable from each other, as are the blacks)? [Answer]

At steady state, air at 200 kpa, 325 k, and mass flow rate of 0.5 kg/s enters an insulated duct having differing inlet and exit cross-sectional areas. the inlet cross-sectional area is 6 cm2. at the duct exit, the pressure of the air is 100 kpa and the velocity is 250 m/s. neglecting potential energy effects and modeling air as an 1.008 kj/kg k, determine ideal gas with constant cp = (a) the velocity of the air at the inlet, in m/s. (b) the temperature of the air at the exit, in k. (c) the exit cross-sectional area, in cm2