2003 AMC 10A Problem 4

It takes Mary

30

minutes to walk uphill

1

km from her home to school, but it takes her only

10

minutes to walk from school to home along the same route. What is her average speed, in km/hr, for the round trip?

Show solution

Solution

Mary walks a total of

2

km in

30 + 10 = 40

minutes. Since

40

minutes is

\dfrac{2}{3}

hour, her average speed is

2 \div \dfrac{2}{3} = 3

km/hr. Thus, the correct answer is A.

Tagged: distance rate and time · harmonic mean