Question

If 20 students in a class failed an exam, the probability of a student selected at random getting pass marks in the exam is 0.6. Calculate the total no. of students in the class.

• A. 45
• B. 55
• C. 50
• D. 60

Answer 1

The correct option is C 50

Let the number of students in the class be $x$.

The probability of students passing the exam = 0.6

Number of students who failed in the exam = 20

Number of students who passed in the exam $=x-20$

$\text{Probability of a student passing the exam}=\frac{\text{Number of students who passed the exam}}{\text{Total number of students in the class}}$

$0.6=\frac{x-20}{x}$

$⟹0.6x=x-20$

$⟹0.4x=20$

$⟹x=50$

The number of students in the class is 50.