A ball is drawn at random from a ball pit containing 8 red balls, 7 yellow balls, 6 green balls, and 5 purple balls. What's the probability that the ball is drawn yellow?

Not enough information - are there 18 yellow balls?

If so, you are trying to calculate the probability at least one of the balls is yellow,

P(no balls are yellow)=P(first ball is non-yellow)×P(second ball is non-yellow)  

P(no yellow)=1230×1129  

P(at least one yellow)=1−P(no yellow)  

You can also calculate the probability of one ball being yellow and them both being yellow:

P(both)=1830×1730  

P(one)=P(first is yellow and second is not)+P(second is yellow and first is not)=1830×1229+1230×1829  

which is just  2×P(first is yellow and second is not).  

Honestly though, this looks just like a homework problem

Step-by-step explanation: