Kaspar has a total of 100 red and green jelly beans. Three times the number of red, decreased by 3 equals double the number of green, increased by 2. How many of each colour are there?
R + G = 100 ⇒ G = 100 - R (1)
R - 3 = 2G + 2 (2)
Sub (1) into (2)
R - 3 = 2(100 - R + 2) simplify
R - 3 = 200 - 2R + 4
R - 3 = 204 - 2R
R + 2R = 204 + 3
3R = 207
R = 207 / 3 = 69
G = 100 - 69 = 31