If it took max 12 hours to do a cleaning job and maggie 4 hours to do the same job how long would it take them if they worked together

The final answer would be 8 hours. :)

So we use the t-distribution to compute a confidence interval for the average age of people using online dating services

Step-by-step explanation:

Confidence interval for a mean.

We have to decide between the t-distribution and the z-distribution.

T-distribution: We use the sample standard deviation.

Z-distribution: We use the population standard deviation.

In this problem:

The average age of those that were using online dating services was 35 years old with a sample standard deviation of 12 years.

So we use the t-distribution to compute a confidence interval for the average age of people using online dating services