In a region of mixed farming, farms keep pigs, cattle or
sheep. there are 77 farms altogether. 19 farms keep only
pigs, 8 keep only cattle and 13 keep only sheep. 13 keep
both pigs and cattle, 28 keep both cattle and sheep and 8
keep both pigs and sheep.
a) draw a venn diagram to show the above information.
b) calculate n(pncns).