posted by Katia on .
I visited a beautiful flower garden yesterday and counted exactly 90 flowers. Each flower was either red or yellow, and the flowers were not all the same color. My friend made the following observation: No matter which two flowers you might have picked, at least one was bound to be red. From this observation, how many were red and how many were yellow?
I guessed on this one and I have the right answers on my online homework. But I don't know how to do it. Could someone help me so I actually know how to do it please?