Ms. A is taking driving test to get her driving license. The probability of passing a test is 0.3 which remains same no matter how many times she takes the test. Let X is a random variable which is the number of tests she takes to get her license.

Patricia Bean

Patricia Bean

Answered question

2022-07-23

Conditional Probability in Geometric Distribution
Ms. A is taking driving test to get her driving license. The probability of passing a test is 0.3 which remains same no matter how many times she takes the test. Let X is a random variable which is the number of tests she takes to get her license.
1) Use conditional probability rule to determine her chance of getting the license on the 6th test starting from her first attempt considering it is known that she has already failed on the first 4 tests.
2) Though one can take the driving test 6 times within a six-month period, he/she can take tests until getting licensed. How many tests is Ms. A expected to take to get the license? What is the standard deviation of the number of tests she takes to get licensed?

Answer & Explanation

losnonamern

losnonamern

Beginner2022-07-24Added 12 answers

Step 1
You need to use the geometric distribution properties:
E ( X ) = 1 p = 1 0.3 = 10 3 V a r ( X ) = 1 p p 2 = 1 0.3 0.3 2 = 70 9
Step 2
And combine these with memorylessness to obtain: E ( X X 4 ) , V a r ( X X 4 )
Hint: E ( X + a ) = E ( X ) + a , V a r ( X + a ) = V a r ( X )

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