Q226 / 270 · NDA 2019 (Phase 1) · Mathematics

For $r \gt 0, f(r)$ is the ratio of perimeter to area of a circle of radius $r$. Then $f(1)+f(2)$ is equal to

  • A
    1
  • B
    2
  • Correct answer
    C
    3
  • D
    4

Solution

$f(r)$ is ratio of perimeter to area of circle of radius $r$. Perimeter of circle $=2 \pi \mathrm{r}$ Area of circle $=\pi \mathrm{r}^2$ $\mathrm{f}(\mathrm{r})=\frac{2 \pi r}{\pi r^2}=\frac{2}{r}$ So, $\mathrm{f}(1)+\mathrm{f}(2)=\frac{2}{1}+\frac{2}{2}=2+1=3$

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

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