Quandaries and Queries Hi I have a task to complete, which is to calculate the mean and standard deviation of something. I have done this but am then asked to write a short explanation of my findings. I know what the mean is about, and I thought I knew what the standard deviation meant too - shows the variation from the mean. However, on a task I completed earlier the feedback I got said 'you need to tell us that it is talking about the middle 66% of the data' - that has thrown me, I don't understand that. Can anyone help me get my head round this??? Many thanks. Rebecca Hi Rebecca, If you have a collection of data from a Normal Distribution then approximately 66% of the data should fall within one standard deviation of the mean. For exmple if the mean is 6 and the standard deviation is 1.2 then approximately 66% of the data is between 6 - 1.2 = 4.8 and 6+1.2 = 7.2 The same approximation is usually true if the data is approximately normally distributed and the data set is reasonably large. By "approximately normal" it is usually enough that a histogram of the data be approximately bell shaped and symmetric. Penny Go to Math Central