The 235u isotope (atomic mass = 235.00) undergoes fission when bombarded with neutrons. however, its natural abundance is only 0.72 percent. to separate it from the more abundant 238u isotope (atomic mass = 238.00), uranium is first converted to uf6, which is easily vaporized above room temperature. the mixture of 235uf6 and 238uf6 gases is then subjected to many stages of effusion. calculate how much more quickly 235uf6 effuses than 238uf6. give the answer as the ratio of rates of 235uf6 to 238uf6 to four decimal places.

The chemical composition of soil varies with depth. an article in communications in soil science and plant analysis describes chemical analyses of soil taken from a farm in western australia. fifty specimens were each taken at depths 50 and 250 cm. at a depth of 50 cm, the average no3 concentration (in mg/l) was 88.5 with a standard deviation of 49.4. at a depth of 250 cm, the average concentration was 110.6 with a standard deviation of 51.5. find a 95% confidence interval for the difference in no3 concentrations at the two depths.