Question

You roll a six-sided die and observe the number showing on the top side when the die comes to rest. What is the probability of observing:

a. an odd number?


b. a number greater than 2?


c. a number less than 7?


d. a prime number?

Answer 1

a. P(O) = ¹/₂ = 0.5

As a percentage, this is 50%

b. P(> 2) = ²/₃ = 0.666...

As a percentage, this is 66.6...%

c. P(< 7) = 1

As a percentage, this is 100%

d. P(prime) = ¹/₂ = 0.5

As a percentage, this is 50%

Explanation:

a.

1, 3 and 5 are odd, 3 of the outcomes

2, 4 and 6 are even, 3 of the outcomes

So, 3 of the 6 possible outcomes are odd and 3 are even;

Thus, the probability of an odd roll is ³/₆ (and the same applies to even);

This can be simplified to ¹/₂

b.

3, 4, 5 and 6 are the outcomes > 2;

1 and 2 are the outcomes ≤ 2;

So, 4 of the 6 possible outcomes are > 2;

Thus, the probability of rolling < 2 is ⁴/₆;

This can be simplified to ²/₃

c.

All outcomes are less than 7 since they are 1, 2, 3, 4, 5 or 6;

This means the probability of rolling less than 7 is ⁶/₆, or simply 1

d.

Prime numbers: 2, 3, 5, 7 ...

The possible prime number outcomes are 2, 3 and 5;

3 of the 6 possible outcomes, therefore, are prime so the probability of rolling a prime is ³/₆ or ¹/₂