Car A leaves the airport at 9:00 am and travels at a constant rate of 30 km per hour. Car B leaves the airport at 9:30 am and travels in the same direction along the same highway at a constant rate of 35 km per hour. At what time will Car B be 20 km ahead of Car A?
Choose the correct choice from the following answers:
A) 4:00 pm  B) 4:30 pm  C) 5:00 pm  D) 5:30 pm  E) 6:00 pm
At 9:30 am, Car A will be 15 km ahead of Car B.   Car B travels at a rate 5 km per hour faster than Car A.   Car B needs to travel 35 km more than Car A in order to be 20 km ahead.   This will take 35 km/5 km per hour=7 hours.   Car B will be 20 km ahead at 4:30 pm.   The answer is 4:30 pm.
<result>B</result>
Car A leaves the airport at 9:00 am and travels at a constant rate of 30 km per hour. Car B leaves the airport at 9:30 am and travels in the same direction along the same highway at a constant rate of 35 km per hour. At what time will Car B be 20 km ahead of Car A?