Household Winter Temperature Often, frequency distributions are reported using unequal class widths because the frequencies of some groups would otherwise be small or very large. Consider the...

I know what the answer is to this question (per the textbook) but I'm not sure how to solve the second part of the question:  determine the standard deviation temperature.  Also, the first part of the question, I calculate 70.28 as the mean but the answer is 70.6.  How should I have rounded that?

Extracted text: Household Winter Temperature Often, frequency distributions are reported using unequal class widths because the frequencies of some groups would otherwise be small or very large. Consider the following data, which represent the daytime household temperature the thermostat is set to when someone is home for a random sample of 750 households. Determine the class midpoint, if necessary, for each class and approximate the mean and standard deviation temperature. Source: Based on data from the U.S. Department of Energy Frequency Midpoint - xi 31 Temperature (°F)(°F) 61-64 65-67 68-69 xi fi 62.5000 1937.50000 67 66.0000 4422.00000 198 195 68.5000 13563.00000 70 71-72 70.0000 13650.00000 120 71.5000 8580.00000 89 50 73-76 74.5000 6630.50000 77-80 78.5000 3925.00000 750 52708.00000 Mean 70.28 | |유