Independent solution

How to solve this Geometric Distribution question

Setup

Setup

Let T be the attempt number of the first success. A single attempt fails with probability 0.75.

Pr(failure)=10.25=0.75\Pr(\text{failure})=1-0.25=0.75

Model

Model

The event T>3 is exactly the event that attempts one through three are all failures.

{T>3}={F1F2F3}\{T>3\}=\{F_1\cap F_2\cap F_3\}

Compute

Compute

Multiply the three independent failure probabilities.

Pr(T>3)=(0.75)3=0.421875\Pr(T>3)=(0.75)^3=0.421875

Answer

Answer

The listed value is 0.42.

0.42(B)\boxed{0.42\quad\text{(B)}}