Question

Bill wants to see how many times he needs to roll a standard number cube before getting a 5. What is the probability that Bill will roll a 5 on his third roll and not before?
a. 125/1296
b. 25/216
c. 1/6
d. 1/2

Answer 1

5/6 • 5/6 • 1/6 = 25/216 the answer is b

Answer 2

Answer:

The answer is b. 25/216

Step-by-step explanation:

Bill wants to see how many times he needs to roll a standard number cube before getting a 5.

p = $\frac{1}{6}$ (on an average: roll 6 times before getting a 5)

The required probability can be found as :

$\frac{1}{5}(\frac{5}{6}* \frac{5}{6}* \frac{5}{6})$

= $\frac{5}{6}* \frac{5}{6}* \frac{1}{6}$

= $\frac{25}{216}$

So, the answer is b. 25/216