Question

. Imagine that you wanted to test the effects of driving at different speeds on the gas mileage of your car. To find out, you drove a distance of 100 miles at many different rates of speed. During your first trip. you drove at exactly 55 miles per hour and calculated that your gas mileage was 20 miles per gallon. During your next trips, you either decreased or increased your rate of speed. Study the graph below from your trips and see if you can identify a control as well as the independent and dependent variables. Explain which axes the dependent and independent variables should be on. Also, what can you conclude from this experiment? How might your car get better gas mileage?

Answer 1

We are asked to study a graph of car performance and give details about the dependent and independent variables. Here is the graph in question:

Our control point is: the info given: 55 miles per gallon gave 20 mi/gallon gas usage. We see clearly that point on the graph, located at (55, 20) on the red line.

Therefore, the gas performance, is the quantity we are studying and it is the "DEPENDENT" variable. As such, it should be graphed on the veritical axis as it is on the graph provided.

The INDEPENDENT variable is the speed we are trying (in the first case the 55 mph (miles per hour) . This variable is what is plotted on the horiontal axis.

Given the shape of the graph: we see it as a line decreasing as we go at higher speeds, the better performance (more miles per gallon) will be obtained as we reduce the speed (going towards 45 miles per hour or even less). Notice that at the beginning of the horizontal axis (for about a 35 mph speed) we see the maximum height of the line at around 27 miles per gallon. So to answer the last question: We could get better gas mileage if we reduce the travelling speed at 35 miles per hour.