CAT 2018 Question Paper Shift 2 Solved Paper

Time taken to cover first $50\mathit{k}\mathit{m}$ at $100\mathit{k}\mathit{m}/\mathit{h}\mathit{r}=1/2\mathit{h}\mathit{r}$
Time taken to cover second $50\mathit{k}\mathit{m}$ at $50\mathit{k}\mathit{m}/\mathit{h}\mathit{r}=1\mathit{h}\mathit{r}$.
Time taken to cover last $50\mathit{k}\mathit{m}$ at $25\mathit{k}\mathit{m}/\mathit{h}\mathit{r}=2$ hr.
When car 2 starts, car 1 has already covered $20\mathit{k}\mathit{m}$.
So, time taken by car 1 to reach $\mathit{B}$ after car 1 starts $=$ total time $-$ time required to travel first 20 $\mathit{k}\mathit{m}$
$=3\mathit{h}\mathit{r}30\mathit{m}\mathit{i}\mathit{n}-12\mathit{m}\mathit{i}\mathit{n}=3\mathit{h}\mathit{r}18\mathit{m}\mathit{i}\mathit{n}$
Distance travelled by car $1=\left(50+50+45\right)=145\mathit{k}\mathit{m}$
Distance from $\mathit{B}=\left(150-145\right)\mathit{k}\mathit{m}=5\mathit{k}\mathit{m}$
Hence, 5 is the correct answer.