The standard deviation of test scores on a certain achievement test is 10.5 . A random sample of 90 scores on this test had a mean of 72.1 . Based on this sample, find a 90% confidence interval for the true mean of all scores. What is the lower limit of the 90% confidence interval?

Idon’t have want a lot more

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.