Question

The marks obtained by 90 students of a school in mathematics out of 100 are given as under:

$\begin{array}{cccccccc}\text{Marks}& 0-20& 20-30& 30-40& 40-50& 50-60& 60-70& \text{70 and above}\\ \text{No. of students}& 7& 8& 12& 25& 19& 10& 9\end{array}$

From these students, a student is chosen at random.

What is the probability that the chosen student

(i) gets 20% or less marks?

(ii) gets 60% or more marks?

Answer 1

ANSWER:
Total number of students = 90
(i) Number of students who gets 20% or less marks = Number of students who gets 20 or less marks = 7
∴ P(Student gets 20% or less marks)
= $\frac{\text{Number of students who gets 20\% or less marks}}{\text{Total number of students}}=\frac{7}{90}$
(ii) Number of students who gets 60% or more marks = Number of students who gets 60 or more marks = 10 +9 = 19
∴ P(Student gets 60% or more marks)
= $\frac{\text{Number of students who gets 60\% or more marks}}{\text{Total number of students}}=\frac{19}{90}$