I had this word problem where I am trying to see whether new version of something is more precise so I know that the formula for test stat is
$$\sum_{i=1}^9 \frac{(yi-\mu)}{x^2}$$$ where $$\sum_{i=1}^9 \frac{(yi-100)}{4}$
in this case I plugged in all the values I had and got this but what confuses me is that how do I get the answer here without knowing yi?