Statistics - properties of the mean

[pointintime]

Homework Statement

not exactly sure were this goes

ok there was a question that my teacher told me i got wrong

the question asked me to compute the mean which I did...

then the question went on to tell me compute the mean with another observation equal to zero

then the part that he drew the line through was my response to this question

Write a sentence about the effect of the zero on Joey's quiz average that mentions this property...

my response

The property that this illustrate of the mean is the observations. Sense the number of observations increased but the sum of the observations stayed the same this brough down the mean by definition...

ok he drew a line threw it and told me it was wrong so my question is how is this wrong?

What would a correct answer include?

Thanks for any Help!

Homework Equations

The Attempt at a Solution

 

[tiny-tim]

Hi pointintime!

my response

The property that this illustrate of the mean is the observations. Sense the number of observations increased but the sum of the observations stayed the same this brough down the mean by definition...

ok he drew a line threw it and told me it was wrong so my question is how is this wrong?

hmm … the English is bad (but I assume it's a translation?), but apart from that, it looks basically correct …

as you say, the mean is the total divided by the number of observations, and the total stays the same but the number of observations increases.

 

[statdad]

The answer the OP gave was probably taken by the instructor to be an observation of the change in this particular case. I think the "property" statement would center on the fact that the mean is not robust (not sensitive, not resistant, depending on the selected terminology); its value can be significantly influenced by a single measurement.