[" 20.A man can hit a bird,once in "3" shots.On this assumption he fires "3" shots."],[" What is the chance that at least one bird is hit? "],[" 21.If the probability that a man aged "60" will live to be "70" is "0.65" ,what is the "],[" probability that out of "10" men,now "60" ,at least "8" will live to be "70?],[" 22.A bag contains "5" white,"7" red and "8" black balls.If four balls are drawn one "],[" by one with replacement,what is the probability that (i) none is white,"],[" (ii) all are white,(iii) at least one is white? "]