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### How do I incorporate a failed trial in my data?

Posted: Thu Jan 15, 2015 9:11 am
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?