Question

In a group of 20 students, 13 students have passed in statistics exam. If a student is selected

at random from the group, what is the probability that the student has failed the statistics exam?

Answer 1

A group of 50 students took an exam.The probability of choosing a student who failed from the group is 1/10.If two students are chosen at random from the group, what is the probability for both of them to pass the exam?

Given the probability of failure (event F) = 1/10 = 0.1

Step-by-step:

Accordingly, the probability of success = 1 - 0.1 = 0.9

So, the probability of getting both the sample drawn to be have passed the exam = 2C2*(0.9)^2(0.1)^0 = 1*0.81*1 = 0.81

Alternately

Probability of failure = 0.1 => 50*0.1 = 5 cases of failure

Accordingly number of students who are likely to pass = 50 - 5 = 45

So, the required probability 45C2/50C2 = (45*44/1*2)/50*49/1*2

= 45*44/50*49 =1980/2450 = 0.808 or 0.81

Answer 2

7/20 = 35%

Explanation:

13 out of 20 students passed which means that 20-13=7 failed. So we have 7/20 which is 35% chance because 7/20 * 5(we need to make 100 to convert to percent) = 35/100=35%