1 answer
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Formula:
CI90 = mean + or - 1.645 (sd/√n)
...where + or - 1.645 represents the 90% confidence interval using a z-table, sd = standard deviation, and n = sample size.
Substituting:
CI90 = 38500 + or - 1.645 (350/√49)
Finish the calculation.
I hope this will help get you started.