First question: if you want to calculate the probability of one event AND another event, you multiply the individual chances. In this example, 1/6 times 1/2 = 1/12.
Second question: same principle. Chance of an even number is 1/2 (2, 4 and 6 are even). times 1/2 = 1/4.
Third question: the chance of the opposite is typically 1-probability, or 100%-probability. So if chance on a penny is 1/5=20%, then the opposite chance is 80%
Fourth question: same. 1/4=25%, opposite is 100%-25% = 75%
