We are dealing with two independent events. This is so because the chance or probability that it it will rain is independent of the chance or probability that there would be a test that you forgot about. If P(A) represents the event that it rains and P(B) represents the event that there is a test that you forgot about, then from the information given,
P(A) = 40/100 = 0.4
P(B) = 40/100 = 0.4
Thus, the odds or probability of tomorrow being a bad day(rain and forgotten test) is P(A) * P(B). Thus,
P(A) * P(B) = 0.4 * 0.4 = 0.16
The answer is 0.16