Science Buddies: "Ask an Expert"

I have a math question regarding findIng the average when one value is zero.

My daughter did an experiment to find which soil additive - none, bone meal or compost - helped sunflowers grow the tallest. In trial 3, neither the compost nor the plain potting soil plant sprouted. Their heights were zero. In analyzing the data, we attempted to find the average height of the plants in each soil type. We did 3 trials. So, for instance, we added the height of each sunflower planted in bone meal on day 15 and divided by 3 to find the average height of a sunflower grown in soil with bone meal.

When it comes time to find the average height of the plants grown in plain potting soil, we got confused. Assuming the plant in trial one grew 4 inches, trial 2 grew 3 inches and trial 3 never sprouted, how do we find the average? Do we throw out the data from trial 3, add 4+3 and divide by 2? Or, do we keep that data, add 4+3+0 and divide by 3?

Your guidance is much appreciated!

Sue

Hi Sue,

Good question! Do you know why the compost and plain potting soil plants didn't sprout in that one trial (e.g., didn't get watered, soil froze, dog knocked the pot over, etc.)? If so, then you could state that you did three trials, one of which didn't work because of reason X. Then, you would report the average from the two trials that did work. (You would still report the three trials for the bone meal additive.)

If you don't know the reason why the compost and potting soil plants didn't sprout in that one trial, then you could include all three trials in your average. In either case, you will want to explain what you did so that the teacher or judge evaluating the project knows what is going in to those averages.

Post back if you have other questions!