4. Why did you take the average of 3 readings--why not 1 reading, or 10?
Turbine experiment.

The reason to take average of 3 readings is its probability of concordance and rendering accuracy in the readings.

Explanation:

In any experiment of analytical research or study, it has always been a practice to take up 3 readings. Usually, the ideology behind taking 3 readings and getting an average of it, came after when the accuracy of the experiment is being judged statistically by the Chi square method test.

Moreover, sometimes when the two consecutive readings in 3 readings are found to coincide or concord, is said to have achieve an accurate results and so the experiments where the sample data is qualitative and not much of quantitative sort, 3 readings are taken average of to achieve an accurate results.

can you attach a picture of the lettuce? : )

3 hours because it is a decent distance.