Question

The cost of a circular table is directly proportional to the square of the radius. A circular table with a radius of 50cm costs £60. What is the cost of a circular table with a radius of 75cm? Show all your working

Answer 1

Answer:

£135 is the correct answer.

Step-by-step explanation:

Let C be the cost of table.

And let R be the radius of table.

Cost of table is directly proportional to square of radius.

As per question statement:

$C\propto R^{2}$ or

$C=a\times R^2 ....... (1)$

where $a$ is the constant to remove the $\propto sign$.

It is given that

$C_1 =$ £60 and $R_1 = 50\ cm$

$C_2 = ?$ when $R_2= 75\ cm$

Putting the values of $C_1$ and $R_1$ in equation (1):

$60=a \times 50^2 ....... (2)$

Putting the values of $C_2$ and $R_2$ in equation (1):

$C_2=a \times 75^2 ....... (3)$

Dividing equation (2) by (3):

$\dfrac{60}{C_2}= \dfrac{a \times 50^2}{a \times 75^2}\\\Rightarrow \dfrac{60}{C_2}= \dfrac{50^2}{75^2}\\\Rightarrow \dfrac{60}{C_2}= \dfrac{2^2}{3^2}\\\Rightarrow \dfrac{60}{C_2}= \dfrac{4}{9}\\\Rightarrow C_2 = 15 \times 9 \\\Rightarrow C_2 = 135$

So, £135 is the correct answer.