Question

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

Marks	0 – 20	20 – 30	30 – 40	40 – 50	50 – 60	60 – 70	70 and above
Number of students	7	8	12	25	19	10	9

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

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) = $\frac{\mathrm{Number}\mathrm{of}\mathrm{students}\mathrm{who}\mathrm{gets}20\%\mathrm{or}\mathrm{less}\mathrm{marks}}{\mathrm{Total}\mathrm{number}\mathrm{of}\mathrm{students}}=\frac{7}{90}$

(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) = $\frac{\mathrm{Number}\mathrm{of}\mathrm{students}\mathrm{who}\mathrm{gets}60\%\mathrm{or}\mathrm{more}\mathrm{marks}}{\mathrm{Total}\mathrm{number}\mathrm{of}\mathrm{students}}=\frac{19}{90}$