The amounts of electricity bills for all households in a particular city have an approximately normal distribution with a mean of $135 and a standard deviation of $25. Let I be the mean amount of...

The amounts of electricity bills for all households in a particular city have an approximately normal distribution with a mean of $135 and a standard deviation of $25. Let I be the mean amount of electricity bills for a random sample of 24 households selected from this city. Find the mean and standard deviation of