Q157 / 270 · NDA 2010 (Phase 2) · Mathematics

The frequency distribution of life of 90 TV tubes whose median life is 17 months is as follows: Figure
What is the lower limit of the median class?

  • A
    10
  • Correct answer
    B
    15
  • C
    20
  • D
    25

Solution

Clearly median class will $15-20$ using formula $\mathrm{M}_{\mathrm{o}}=l+\frac{\frac{N}{2}-c . f .}{f} \times i$ $\text { Also } \quad \begin{aligned} 54+x+y & =90 \\ x+y & =36...(i) \end{aligned}$ $\begin{array}{rlrl}\text { Again } & & 17 & =15+\frac{45-15-x}{35} \times 5 \\ \Rightarrow & & 2 & =\frac{30-x}{y} \\ \Rightarrow & x & =30-14=16 \\ \Rightarrow & y & =20\end{array}$

Hence, the correct answer is option: 'B'.

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