8and2/7+3and 1/3=>(8*7+5)/7+(3*3+1)/3=>61/7+4/3=>183/21+28/21=>211/21.
Are you familiar with z-scores? According to the definition,
(given numerical value) - (mean)
z = ---------------------------------------------
standard deviation
Thus, with the given numerical value equal to 410 and the std. dev. equal to 75, the corresponding z-score is
410-500 -90
z = --------------------- = --------------- = -1.2
75 75
Use a table of z-scores to determine the area under the standard normal curve to the left of z = -1.2. Your result is the probability that a given family chosen at random spends less than $410 per month.
If you would like to calculate the arithmetic mean, geometric mean, and harmonic mean from the following averages, you can calculate this using the following steps:
averages: 56.4, 59.8, 55.8
the number of values: 3
arithmetic mean:
(56.4 + 59.8 + 55.8) / 3 = 57.33
geometric mean:
(56.4 * 59.8 * 55.8)^(1/3) = 57.31
harmonic mean:
3 / (1/56.4 + 1/59.8 + 1/55.8) = 57.28