The marks obtained by 90 students in mathematics out of 100 are given below.

Marks 0−20 20−30 30−40 40−50 50−60 60−70 70 and above

No. 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?

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Solution

Total number of students = 90
(i) Number of students who scored 20% marks or less = 7.
Let E₁ be the event that selected student got 20% marks or less.Then,

P(E₁) = $\frac{7}{90}$
(ii) Number of students who scored 60% marks or more = (10 + 9 ) = 19.
Let E₂ be the event that selected student got 60% marks or more.Then,

P(E₂) = $\frac{19}{90}$

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Similar questions

Marks	0−20	20−40	40−60	60−80	80−100
No. of students	8	15	32	26	9

Marks	10−20	20−30	30−40	40−50	50−60	60−70	70−80	80−90	90−100
Number of Students	4	10	16	22	20	18	8	2	5

The table given below shows the marks obtained by 140 students of a class in a test with maximum marks 100.

A student of the class is selected at random. Find the probability that this student gets

Marks	10−20	20−30	30−40	40−50	50−60	60−70	70−80	80−90
No. of students	7	13	20	25	10	8	6	1

The marks scored by 60 students in a mathematics test are given below.

Marks (X)	10	20	30	40	50	60
No. of students (f)	8	12	20	10	7	3

Find the Variance and Standard Deviation of the marks.

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