Question

David drives from his home to the airport to catch a flight. He drives $35$ miles in the first hour, but realizes that he will be $1$ hour late if he continues at this speed. He increases his speed by $15$ miles per hour for the rest of the way to the airport and arrives $30$ minutes early. How many miles is the airport from his home?

$140$

$175$

$210$

$245$

$280$

Solution:

Let $d$ be the remaining distance after one hour and $t$ the remaining time until the flight. At $35$ mph he would be an hour late, so $d=35(t+1).$ At $50$ mph he is half an hour early, so $d=50\left(t-\tfrac12\right).$

Setting these equal gives $35t+35=50t-25,$ so $t=4$ and $d=175.$

The total distance is $175+35=210$ miles.

Thus, the correct answer is C.

2014 AMC 12A Problem 11

Solution:

Problem 11 in Other Years