For urn A, you will always be given the exact percentage of red marbles. For urn B, you will receive advice from someone who wants to help you who has estimated the percentage of red marbles in urn B. There are two sources,
The optimist tends to overestimate the number of winning (red) marbles.
The pessimist tends to underestimate the number of winning (red) marbles in the urn.
These people are trying to help you, but they do not know the exact percentages; they make their estimates by shaking the jar, looking through the clear glass, and estimating the percentage by eye.
In each case you decide whether you would rather choose urn A, which has a known percentage of
red marbles or from urn B, about which you have estimates of the percentage of winning (red) marbles.