A Science test and an English test were administered to a class of 30 ...
Step I: Define Non-event
1 student is selected at random out of a class of 30 students. The event in this question is that the selected student has passed in at least one of the two tests.
Since a majority of the students have passed at least one of the two sets (it is given that only 10% of the students have failed in both tests), the number of ways in which the event can occur will be far more than the number of ways in which the non-event can occur.
So, this question will be solved more quickly through the non-event method.
The non-event in this case will be that the selected student has failed in both the tests.
So, the probability event equation is:
P(Student has passed at least 1 test) = 1 – P(Student has failed both tests)
Step II: Find n, the number of ways in which all outcomes can occur
Now, the total number of ways in which 1 student can be selected out of 30 students
= 30C1 = 30
So, n = 30
Step III: Find x, the number of ways in which the Non-event can occur
The non-event is the selection of a student who has failed both tests.
From the question statement, we know that
Number of students who failed both tests = 10% of all students
= 10% of 30 = 3
Thus, the non-event occur if one of out of these 3 students is selected.
Number of ways in which this can happen = 3C1 = 3
So, x = 3
Step IV: Calculate probability for Non-event
P(Student has failed both tests)
Step V: Probability (Event) = 1-Probability (Non-event)
Now, let’s put the value of P (Non-event) in the probability event equation:
P(Student has passed at least 1 test) = 1 – P(Student has failed both tests)
Step V: Probability (Event) = 1-Probability (Non-event)
Now, let’s put the value of P (Non-event) in the probability event equation:
P(Student has passed at least 1 test) = 1 – P(Student has failed both tests)
Answer: Option (E)