1) A driver wants to set a new record on a $50 \mathrm{~km}$ route: to complete it at an average speed of $100 \mathrm{~km} / \mathrm{h}$. Due to some technical issues, he spends 40 minutes on the first $25 \mathrm{~km}$. At what speed must he travel the rest of the route (at a constant speed) to succeed in his goal?
(A) No speed will allow him to do so,
(B) $50 \mathrm{~km} / \mathrm{h}$,
(C) $100 \mathrm{~km} / \mathrm{h}$
(D) 150 $\mathrm{km} / \mathrm{h}$, (E) $200 \mathrm{~km} / \mathrm{h}$
1. The answer is $(\mathbf{A})$.

If the driver wants to travel $50 \mathrm{~km}$ at an average speed of $100 \mathrm{~km} / \mathrm{h}$, the total time required to cover this distance must be half an hour. On the other hand, he has already taken more than half an hour to cover just the first half of the journey, and no matter what the average speed is for the second half, the total travel time will be strictly greater than half an hour.