Answer:
The formula for the lower and upper bounds for a confidence interval for the difference between to proportions is given in the picture.
In this case the p1 is going to be the proportion of units of gold wire that met the specification. p2 is going to be the proportion of aluminum wire that met the specification. The z for a 99% confidence interval is going to be 2. 575. n1 is going to be the total number of units of gold wire sampled and n2 is going to be the total number of units of aluminum wine sampled.
p1 = 70/83 = 0.843
p2 = 98/115 = 0.852
The difference between them is 0.009.
The value of the square root that is multiplying the z is: 0.052
The lower bound is going to be -0.043
the upper bound is going to be 0.061
The confidence interval is:
( -0.043, 0.061 )
