The acidity of soils is measured by a quantity called the ph, which may range from 0 (high acidity) to 14 (high alkalinity). a soil scientist wants to estimate the average ph for a large field by randomly selecting n core samples and measuring the ph in each sample. although the population standard deviation of ph measurements is not known, past experience indicates that most similar soils have a ph value between 5.9 and 9.5. suppose the scientist would like the sample mean to be within 0.15 of the true mean with probability 0.90. what is the minimum number of core samples the scientist should take? (round your answer up to the nearest whole number.)