Probability Practice Test 2

For at least 3 trials, he has to fail at the first 2 attempts and then after that it does not make a difference if he fails or wins at the 3rd or the subsequent attempts.
Chance of success in any attempt =

1

4

⇒ Chance of failure =

3

4

⇒ Chance of failure in the first 2 attempts =(

3

4

)2
Chance of success at any attempt =

1

4

⇒ Chance of failure =

3

4

⇒ Chance of failure in the first 2 attempts =(

3

4

)2=

9

16