Answer: 1015
Step-by-step explanation:
Given :In a previous testing of wine specimens, lead levels ranging from 50 to 700 parts per billion were recorded.
Here , Range = 700-50=650 [∵ Range = Max-Min]
According to the thumb rule , the range is approximately 4 times the standard deviation.
Let
be the standard deviation, then

Thus, 
For confidence interval of 95% , the critical z value = 
Formula to find the sample size : 
Now, for the margin of error of E=
, we have

Hence, the required sample size = 1015