CAT 2020 Exam Shift 2 Solved Paper

Let the length of the racetrack be $\mathit{D}$.
When A covers $\mathit{D}\mathit{k}\mathit{m},\mathit{B}$ covers $\left(\mathit{D}-45\right)\mathit{k}\mathit{m}$ and $\mathit{C}$ covers $\left(\mathit{D}-90\right)\mathit{k}\mathit{m}$
When B covers D $\mathit{k}\mathit{m},\mathit{C}$ covers $\left(\mathit{D}-50\right)\mathit{k}\mathit{m}$
The ratio of the speeds of the racers is same as the ratio of the distance travelled in a given time period.
Ratio of speed of $\mathit{B}$ and $\mathit{C}$ is $\Rightarrow \frac{\mathit{D}}{\mathit{D}-50}=\frac{45}{40}$
$\Rightarrow 40\mathit{D}=45\mathit{D}-50\times 45$
$\Rightarrow \mathit{D}=450$