A contractor is uncertain of the precise total costs for either materials or labor for a project. In addition, the total line of credit for financing the project is $260,000, and the contractor wants to know the probability that total costs exceed $260,000. It is believed that material costs can be represented by a normally distributed random variable with mean $100,000 and standard deviation $10,000. Labor costs are $1,500 a day, and the number of days needed to complete the project can be represented by a normally distributed random variable with mean 80 and standard deviation 12. Assuming that material and labor costs are independent, what are the mean and standard deviation of the total project cost (materials plus labor)? In addition, what is the probability that the total project cost is greater than $260,000?

Definition Definition Measure of central tendency that is the average of a given data set. The mean value is evaluated as the quotient of the sum of all observations by the sample size. The mean, in contrast to a median, is affected by extreme values. Very large or very small values can distract the mean from the center of the data. Arithmetic mean: The most common type of mean is the arithmetic mean. It is evaluated using the formula: μ = 1 N ∑ i = 1 N x i Other types of means are the geometric mean, logarithmic mean, and harmonic mean. Geometric mean: The nth root of the product of n observations from a data set is defined as the geometric mean of the set: G = x 1 x 2 ... x n n Logarithmic mean: The difference of the natural logarithms of the two numbers, divided by the difference between the numbers is the logarithmic mean of the two numbers. The logarithmic mean is used particularly in heat transfer and mass transfer. ln x 2 − ln x 1 x 2 − x 1 Harmonic mean: The inverse of the arithmetic mean of the inverses of all the numbers in a data set is the harmonic mean of the data. 1 1 x 1 + 1 x 2 + ...