Allen S. answered • 01/21/15

Tutor

New to Wyzant
Patient tutor for high school aged and lower students.

Ji-Kyung,

Probability is computed using the fractional notation of each possibility:

For instance, the probability of both being heads or both being tails independently of each other would be:

1/2 * 1/2 = 1/4

If the probability of both being heads is 1/4, then the probability of at least one of the coins being tails is the two fractional probabilities added together minus the probability that both will be heads: 1 - 1/4, or 3/4, or .75, or 75%

For your second question, 2 4-sided dice.

The probability of both dice showing 1 is 1/4 * 1/4 = 1/16

That means the probability of one die showing 1 is : 1/4 + 1/4 - 1/16

1/2 -1/16

7/16 is the probability that at least one die will show 1.