Skewed data and 3 median line

[hardworker]

Just wondering how much does the mean have to differ from the median to be a positively skewed data or negatively skewed data cause the teacher at school told us if it differs by a minor value it still remains symmetric but how much can it differ by? eg i got a data with a mean 81.4 and a median with 80 he told us that its still symmetrical but i thought it would've been slightly positively skewed. 

Also when you draw the 3 median line regression does it have to go through the middle median and when do you know how to draw it above or bellow the original line from the lower and upper median.

Thanks in advance.

[Stick]

Just wondering how much does the mean have to differ from the median to be a positively skewed data or negatively skewed data cause the teacher at school told us if it differs by a minor value it still remains symmetric but how much can it differ by? eg i got a data with a mean 81.4 and a median with 80 he told us that its still symmetrical but i thought it would've been slightly positively skewed.

To be really honest, I don't think I ever used the mean and median to determine whether a data set is skewed or not. Generally speaking, the shape of a histogram is enough for you to determine this.   

Also when you draw the 3 median line regression does it have to go through the middle median and when do you know how to draw it above or bellow the original line from the lower and upper median. 

Have you learnt the formula for a 3 median regression line? I found it easier than sliding my ruler and doing all that jazz.

[Daenerys Targaryen]

Wasnt the three median regression line joining the end medians with the ruler, then moving the ruler 1/3 of the distance towards the middle median. Maintaing its parallel to the line that joins the left and right

[Stick]

Yeah, but if you know me, I hate doing that sort of stuff, so I used the formula instead.

[brenden]

Yeah I just used the shape. The median/mean will have slight variances even if the data is symmetric.

[hardworker]

I get it now thanks everyone