There are 40 rainbows. Rainbows are only made out of up to 4 colors: Red, Orange, Blue, and Purple. 25 of the rainbows have red, 30 of them have orange, 33 of them have blue, and 35 of them have purple. Prove that there exists at least 3 rainbows such that each of the rainbows have all 4 of the possible colors.
I'm pretty sure this is just a basic application of the Pigeonhole Principle, but I'm not really sure how to get started. The holes I have right now are the 4 colors. Any help would be greatly appreciated.
Call each instance of a color in a rainbow a rainbow-color. The $40$ rainbows contain altogether $25+30+33+35=123$ rainbow-colors. If each rainbow contained only $3$ colors, that would account for only $120$ rainbow-colors. No rainbow can account for more than $4$ rainbow-colors. Can you finish it now?