[填空题]
John decided to build a stone fenci g2 sup dp/y:4j.tf2de around h*n+ur)e oq9e8:pux gais house and lay a stone walkway. John ordered a large bag of stones and first chose a random a sample of 50 stones for measuring. He measured the diameters of the stones correct to the nearest centimetre. The following table shows th e:pu*eq xgru)a+o 8n9e frequency distribution of these diameters.
1. Find the value of (1) the mean diameter of these stones; ≈ cm
(2) the standard deviation of the diameters of these stones.
John assumes that the diameters of all the stones from this bag are normally distributed with a mean 16 $\mathrm{~cm}$ and a standard deviation of 1.1 $\mathrm{~cm}$ John sorts all stones by their diameter size.≈ cm
2. John selects the largest stones, with diameters of 18 $\mathrm{~cm}$ or greater, to use for the stone walkway. Estimate the percentage of stones used.≈ %
3. John selects small stones, which have a diameter less than x $\mathrm{~cm} $ to use for a walkway border. The small stones account for 5 $\%$ of the total number of stones. Calculate the value of x .
4. John selects medium stones to use the stone fence. Estimate the percentage of medium stones with diameter more than x $\mathrm{~cm}$ from part (c) and less than 18 $\mathrm{~cm}$ .≈ %
5. John estimates that there are about 10000 stones in total. Estimate the number of large stones.
