2017 AMC 10 A

Complete problem set with solutions and individual problem pages

Problem 9 Easy

Minnie rides on a flat road at 20 kilometers per hour (kph), downhill at 30 \rm kph, and uphill at 5\rm kph. Penny rides on a flat road at 30 \rm kph, downhill at 40 \rm kph, and uphill at 10 \rm kph. Minnie goes from town A to town B, a distance of 10 \rm km all uphill, then from town B to town C, a distance of 15 \rm km all downhill, and then back to town A, a distance of 20 \rm km on the flat. Penny goes the other way around using the same route. How many more minutes does it take Minnie to complete the 45-\rm km ride than it takes Penny? (2017 AMC 10A Problem, Question#9)

  • A.

    45

  • B.

    60

  • C.

    65

  • D.

    90

  • E.

    95

Answer:C

The distance from town A to town B is 10\rm km uphill, and since Minnie rides uphill at a speed of 5 \rm kph, it will take her 2 hours. Next, she will ride from town B to town C, a distance of 15 \rm km all downhill. Since Minnie rides downhill at a speed of 30 \rm kph, it will take her half an hour. Finally, she rides from town C back to town A, a flat distance of 20 \rm km. Minnie rides on a flat road at 20 \rm kph, so this will take her 1 hour. Her entire trip takes her 3.5 hours. Secondly, Penny will go from town A to town C, a flat distance of 20 km. Since Penny rides on a flat road at 30 \rm kph, it will take her \dfrac{2}{3} of an hour. Next Penny will go from town C to town B, which is uphill for Penny. Since Penny rides at a speed of 10 \rm kph uphill, and town C and B are 15\rm km apart, it will take her 1.5 hours. Finally, Penny goes from Town B back to town A, a distance of 10 \rm km downhill. Since Penny rides downhill at 40 \rm kph, it will only take her \dfrac{1}{4} of an hour. In total, it takes her \dfrac{29}{12} hours, which simplifies to 2 hours and 25 minutes. Finally, Penny's 2 Hour 25 Minute trip was (\rm C)65 minutes less than Minnie's 3 Hour 30 Minute Trip.