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NDA 2020
Exam
NDA
Year
2020
Subject
Mathematics
Chapter
Statistics

NDA 2020 · Mathematics · Statistics

The numbers 4 and 9 have frequencies x and (x-1) respectively. If...

The numbers 4 and 9 have frequencies xx and (x−1)(x-1) respectively. If their arithmetic mean is 6 , then what is the value of xx ?

Options

  1. A2
  2. B3
  3. C4
  4. D5

Correct answer

B. 3

Step-by-step solution

Arithmetic mean = Sum of data  Number of data =\frac{\text{ Sum of data }}{\text{ Number of data }}6=4×x+9(x−1)(x+x−1)6(2x−1)=4x+9x−912x−6=13x−9x=9−6=3.\begin{aligned} & 6=\frac{4 \times x+9(x-1)}{(x+x-1)} \\ & 6(2 x-1)=4 x+9 x-9 \\ & 12 x-6=13 x-9 \\ & x=9-6=3 . \end{aligned}$$
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