3

Part of 2009 Swedish Mathematical Competition

Problems(1)

probabiblity 1/4 when extracting 2 balls from a urn of yellow and greens

Source: 2009 Swedish Mathematical Competition p3

An urn contain a number of yellow and green balls. You extract two balls from the urn (without adding them back) and calculate the probability of both balls being green. Can you choose the number of yellow and green balls such that this probability to be

\frac{1}{4}

probabilitycombinatorics