Question 304709
Hello!
Sorry for your wait, I hope this makes up for it :)
You know that each ball has an equal chance of being picked out of the bag.
You also know that there are 10 odd-numbered balls in there and 9 even-numbered ones. 
The known equation for probability is (number of successes)/(total number)
So, the probability that you will pick an even-numbered ball is 9/19, or 0.474%
That's it!