- #1

lawsonj

- 9

- 0

## Homework Statement

"Julie drives 100 mi to her Grandmother's house. On the way, she drives half the distance at 40 mph and half the distance at 60 mph. On her return trip, she drives half the time at 40 mph and half the time at 60 mph."

## Homework Equations

a. "What is Julies average speed on the way to Grandmother's house?"

b. "What is her average speed on the return trip?"

## The Attempt at a Solution

The book says a. is 48 m/h and b. is 50 m/h...but i don't exactly know how this was found.

I am thrown by the second question BC 1. How could she possibly know what "half the time" is if she doesn't know her average velocity? 2. how do you find delta-t from this information?

By working out delta-t from the first question, I figured that the trip (50% 40 m/h & 50% 60 m/h) took 2.083 hrs total, which would make 1/2delta-t = 1.0417 hr. This is as close as I could get to determining HOW to find 1/2delta-t in order to calculate what her av. speed is traveling "half the time" at 60 and half the time at 40.

my instinct says that the answer to a. is 50 m/h but the book says otherwise...

how do you find the answer to b. without knowing delta-t?

please help, sincerely,

someone bad at math