I know this might be stupid but I can’t help thinking about solving the problem of variance of weights of children given the variance of weighing scale in the following manner :-

- We add 250 g (variance of weighing scale) to all sample weights. We say it Wj
- Also, we subtract 250g from all sample weights. We say it Wk
- Now we subtract Wk from Wj and divide it by 10 (No of samples)

What would this mean? What have we computed?