Question

A family is traveling in a car at a constant average speed during a road trip. The function d(t)=70t+620 models the distance d, in miles, the family is from their house t hours after starting to drive on the second day of the road trip.

A) At what average speed is the family's car traveling?
-Explain
B) What is the distance between the family's house and the point where they started driving on the second day
-Explain

Answer 1

A. 70 miles per hour B. 620 miles from home

Explanation:

This function is a linear equation, following the slope-intercept form of a line. This standard form is y = mx + b, where m is the slope and b is the y-intercept. The slope of a line is the rate at which the steepness of the line is changing. The y-intercept is where the function is "starting".

In our case, the number in the rate of change position is 70. It is being multiplied by t. If t = 1, that means that after 1 hour, we have gone 70 miles. If t = 2, that means after 2 hours we have gone 140 miles. If t = 3, that means that after 3 hours, we have gone 210 miles; etc. That number in the slope position represents the rate at which you are traveling PER HOUR; the slope.

The "starting" position of day 2 is found in the y-intercept. Replacing x with 0, meaning NO time has gone by at all, at the beginning of the second day, we are starting 620 miles from home.