A man arrives home at midnight drunk. In order to placate his partner he decides to present her with some flowers picked from the flower bed. The flower bed contains a randomly placed selection of 10 tulips, 15 daffodils and 5 assorted weeds. He picks at random 3 flowers. Use a probability tree to determine the probability that:
a. They are all weeds;
b. The bunch contains two tulips and one daffodil;
c. The bunch contains one tulip, one daffodil and one weed.