You want to be able to estimate the average IQ of people in Winston-Salem. You would be satisfied knowing the average IQ plus-or
-minus 5IQ points(using a 90% confidence interval). The standard deviation for IQ tests is typically 15 points; so you’ll use that as a guideline. How many people would you need to survey in order to be able to estimate the average to your desired degree of accuracy?
48÷2=24, 24 is half of 48, 24 days is half of the amount of time as 48 days, so if it takes 48 days for the whole lake to be covered, it would take 24 days to cover half of it.