[" 7.If "12" identical balls are to be placed in "3" different boxes,"],[" then the probability that one of the boxes contains excatly "],[3" balls,is "],[[" (a) "(55)/(3)((2)/(3))^(11)," (b) "55((2)/(3))^(10)," (c) "220((1)/(3))^(12)," (d) "22((1)/(3))^(11)]]