Skip to main content

2018 AMC 12B Problem 2

Problem 2 of 25EasierArithmetic

Sam drove 9696 miles in 9090 minutes. His average speed during the first 3030 minutes was 6060 mph (miles per hour), and his average speed during the second 3030 minutes was 6565 mph. What was his average speed, in mph, during the last 3030 minutes?

Answer choices

Show solution

Solution

In the first 3030 minutes Sam covered 60⋅12=3060\cdot\tfrac12=30 miles, and in the second he covered 65⋅12=32.565\cdot\tfrac12=32.5 miles. The last 3030 minutes covered 96−30−32.5=33.596-30-32.5=33.5 miles, so the speed was 33.512=67 mph. \dfrac{33.5}{\frac{1}{2}}=67\text{ mph}. Thus, the correct answer is D.
AoPS wiki

Tagged: distance rate and time

More practice