Question

Some students of class X planted trees in school surroundings as a part of Green India project.

Their contribution is shown in the following frequency distribution.

No of trees 10-20 20-30 30-40 40-50 50-60

No of

students

8 5 12 11 4

Find median trees planted by school students.
​

Answer 1

Solution :-

No. of trees Fi CF

10 - 20 8 8

20 - 30 5 13

30 - 40 12 25

40 - 50 11 36

50 - 60 4 40

40

Here , n = 40 .

So,

→ (n/2) = 20 .

Then,Cumulative frequency greater than 20 is 25, corresponds to the class 300 - 400.

Therefore,

→ Class 30 - 40 is the median class.

Now,

• Median = l + [{(n/2) - cf} / f] * h

from data we have :-

• l = lower limit of median class = 30
• n = total frequency = 40
• cf = Cumulative frequency of class before median class = 13 .
• f = frequency of median class = 12 .
• h = size of class = 10 .

Putting all value we get :-

→ Median = 30 + [(20 - 13)/12] * 10

→ Median = 30 + (70/12)

→ Median = 30 + 5.83

→ Median = 35.83 ≈ 35 trees (Ans.)

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