Question

& Marks obtained by a group of 40 students in a test
are given below. Find the missing frequency
and if their mean is 18.
5
10 15 20 25 30
No. of students 6
4
12 5
4​

Answer 1

Answer:

0.

∴6+a+16+13+b=40

⇒a+b=15...(1)

The mean of the given data is

40

5×6+6a+7×16+8×13+9b

⇒

40

30+6a+112+104+9b

=7.2

⇒246+6a+9b=288

⇒6a+9b=42

⇒2a+3b=14...(2)

From (1), we get b=15−a. Substitute this value in (2)

∴2a+3(15−a)=42

⇒2a+45−3a=42⇒a=3

∴b=15−a=15−3=12

Answer verified by Toppr

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