In New Zealand in 1946 there were two different coins of value two shillings. These were 'normal' kiwis and 'flat back' kiwis, in the ratio 3 : 1. From a very large batch of 1946 two shilling coins, five were selected at random with replacement. Find the probability that: (i) two were 'flat backs' (ii) at least 3 were 'flat backs' (iii) at most 3 were 'normal' kiwis.