M. T. Smith travels the eastern United States as a sales representative for a textbook publisher. She is paid on a commission basis related to volume. Her quarterly earnings over the last 3 years are given below.
| 1st Quarter | 2nd Quarter | 3rd Quarter | 4th Quarter | |
| Year 1 | $10,000 | $ 5,000 | $25,000 | $15,000 |
| Year 2 | 20,000 | 10,000 | 20,000 | 10,000 |
| Year 3 | 30,000 | 15,000 | 45,000 | 50,000 |
- Calculate separately M. T.’s average earnings in each of the four quarters.
- Calculate separately M. T.’s average quarterly earnings in each of the 3 years.
- Show that the mean of the four numbers you found in part (a) is equal to the mean of the three numbers you found in part (b). Furthermore, show that both these numbers equal the mean of all 12 numbers in the data table. (This is M. T.’s average quarterly income over 3 years.)
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