Question 1177048
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Hi
the standard deviation of the population of completion times is 10.2 minutes
to be 90% confident that their estimate is within 2.0minutes of μ:

ME ={{{ z*sigma/sqrt(n)}}}   0r  {{{ n = ((z*sigma)/ME)^2}}}

n = {{{((1.645*10.2)/2)^2}}} = 70.384   0r 71 sample size (rounding up to nearest whole number)

Wish You the Best in your Studies.
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