for the first one:
You take the number of plain chips and divide it by 3, then multiply by four. You do this because there is a 4 to 3 ratio of hot to plain chips.
42 / 3 = 14, 14 x 4 = 56.
Second one:
Birds (usually) have two wings for each beak. Why? I don't know, ask Darwin. There is a 2:1 (two to one) ratio of wings to beaks.
Third:
50 flaps per second, 60 seconds in a minute. 50 x 60 = 3000.
45,000 / 3000 = 15 minutes.
Fourth:
56 + 120 + 24 = 200
56 / 200 = 28% of the students ate pasta