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Mathematics

The mean of observations, given in the adjoining table, is 20, the value of a is :
x f fx
10 10
20 a
30 10
20
30
10
25

Statistics

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Answer

By formula,

Mean = $\dfrac{Σfx}{Σf}$

x	f	fx
10	10	100
20	a	20a
30	10	300
Total	Σf = 20 + a	Σfx = 400 + 20a

Substituting values we get :

$\Rightarrow 20 = \dfrac{400 + 20a}{20 + a}$

⇒ 20(20 + a) = 400 + 20a

⇒ 400 + 20a = 400 + 20a

The above equation cannot be solved, so the question is incorrect.

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The monthly income of a group of 320 employees in a company is given below :
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(ii) the number of employees whose income is below ₹ 8500.
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