CAT 2019 Shift 2 Paper

Time taken by cyclist to cover the distance $\mathit{A}\mathit{B}=60\mathit{m}\mathit{i}\mathit{n}$
Given, starting from 10: 01 am, every minute a motor cycle leaves $\mathit{A}$ and moves towards $\mathit{B}$. Forty-five such motor cycles reach B by $11\mathit{a}\mathit{m}$.
Also, the speed of all the motor cycles is same.
That means that the 45 th moto cycle which started at 10: 45 am, reached B exactly at 11 am. Rest all reached B some time before B.
Therefore, each motor cycle takes 15 min to cover the distance $\mathit{A}\mathit{B}$.
Now, if the cyclist doubles his speed, then he will reach B in 30 min i.e. at 10: 30 am.
So, the 15 th motor cycle (started at 10: 15 am from A) would be the last motor cycle to reach point $\mathit{B}$ at 10: 30 am.
Hence, there will be 15 motor cycles would have reached $\mathit{B}$ by the time the cyclist reached B.