There are 2 white and 1 black balls in the urn. Remove all balls one by one. What is the probability that the 3rd ball is white?

A total of 6 options are possible as to what order will be when three balls are retrieved. This number is equal to the number of permutations of three elements.
n = 3! = 6;
The last one can get any of the two white balls. These are two options and in each of these options the previous black and white balls can be interchanged. There will be m = 4 favorable outcomes in total.
The probability that the third ball will be white:
P = m / n = 4/6 = 2/3 = 0.667.
Answer: 0.667.