Answer:
The minimum sample size required is 25 so that margin of error is no more than 3 minutes.
Explanation:
We are given the following in the question:
Mean, μ = 42 minutes
Standard Deviation, σ = 9 minutes.
We want to build a 90% confidence interval such that margin of error is no more than 3 minutes.
Formula for margin of error:


Putting values, we get.

Thus, the minimum sample size required is 25 so that margin of error is no more than 3 minutes.