The mean amount spent by all customers at organic food market is estimated to be $48, and the standard deviation is estimated to be $12. According to Chebyshev's Theorm at least what percentage of customers would be expected to spend between $27 and $69? Express your answer to two decimal places of accuracy.
For any number k greater than 1 at least (1-1/k2) of the values for any distribution lie within k standard deviations of the mean.
Please show answer and calculations in detail.