Question

$
  {\text{The cost of fencing a circular field at the rate Rs 24 per metre is Rs 5280}}{\text{. The field is to be }} \\
  {\text{ploughed at the rate of Rs}}{\text{. 0}}{\text{.50 per }}{{\text{m}}^2}.{\text{ Find the cost of ploughing the field}}{\text{. (Take }}\pi {\text{ = }}\dfrac{{22}}{7}{\text{) }} \\
  {\text{A}}{\text{. Rs 1278}} \\
  {\text{B}}{\text{. Rs 1437}} \\
  {\text{C}}{\text{. Rs 1925}} \\
  {\text{D}}{\text{. Rs 2870}} \\
$

Answer 1

\[
  {\text{Given, Total cost of fencing the circular field }} = {\text{Rs }}5280 \\
  {\text{Rate of fencing the circular field = Rs 24/m}} \\
  {\text{Rate of ploughing the circular field = Rs 0}}{\text{.5/}}{{\text{m}}^2} \\
  {\text{Since, we know that fencing occurs around the circumference and ploughing is }} \\
  {\text{done on the area of the circular field}}{\text{.}} \\
  {\text{Therefore, Circumference of the circular field = }}\dfrac{{{\text{Total cost of fencing the circular field}}}}{{{\text{Rate of fencing the circular field }}}} \\
  {\text{If 'r' is the radius of the circular field, then its circumference is 2}}\pi {\text{r where }}\pi {\text{ = }}\dfrac{{22}}{7} \\
   \Rightarrow {\text{2}}\pi {\text{r}} = \dfrac{{5280}}{{24}} \Rightarrow r = \dfrac{{5280}}{{24 \times 2\pi }} = \dfrac{{5280 \times 7}}{{24 \times 2 \times 22}} = 35{\text{ }}m \\
  {\text{So, the radius of the circular field is 35 metres}}{\text{.}} \\
  {\text{Area of the circular field = }}\pi {{\text{r}}^2} = \dfrac{{22}}{7} \times {35^2} = 3850{\text{ }}{m^2} \\
  {\text{Now, Total cost of ploughing = (Area of the circular field)}} \times {\text{(Rate of ploughing the circular field)}} \\
   \Rightarrow {\text{Total cost of ploughing = 385}}0 \times 0.5 = {\text{Rs }}1925. \\
  {\text{Therefore, Option C is correct}}{\text{.}} \\
    \\
  {\text{Note - In these type of problems, simply a common parameter(which is radius here) is calculated }} \\
  {\text{from the given data which will help to relate between the two processes which are }} \\
  {\text{fencing(circumference based) and ploughing(area based)}}{\text{. }} \\
 \]