Consider the question. In a field of 500 clovers, 20% have four leaves and one quarter of these are purple clovers. Assuming these proportions are exactly correct, how many clovers in the field are both purple and four-leaved?
 If the answer is '25'; explain the reasoning:
There are 500 / 5 = 100 four leaf clovers. There are 100 / 4 = 25 purple four leaf clovers.