The distance from City A to City B is 100 miles. While driving from City A to City B, Bob drives at a constant speed of 40 miles per hour. Alice leaves City A 30 minutes after Bob. What is the minimum constant speed in miles per hour that Alice must exceed in order to arrive in City B before Bob?	Choose the correct choice from the following answers.
A) 45  B) 48  C) 50  D) 52  E) 54
The time it takes Bob to drive to City B is 100 / 40= 
<gadget id="calculator">100 / 40</gadget>
<output>5/2 = around 2.5</output>
2.5 hours.   Alice needs to take less than 2 hours for the trip.   Alice needs to exceed a constant speed of 100 / 2= 
<gadget id="calculator">100 / 2</gadget>
<output>50</output>
50 miles per hour.   The answer is 50.
<result>C</result>
The distance from City A to City B is 100 miles. While driving from City A to City B, Bob drives at a constant speed of 40 miles per hour. Alice leaves City A 30 minutes after Bob. What is the minimum constant speed in miles per hour that Alice must exceed in order to arrive in City B before Bob?