A circular swimming pool has a radius of 20 feet. A fence is going to be built so that there is a 4-foot space around the entire pool. What is the length of the fence? Sunitha solved the problem as shown. A circle with radius 20 feet. A larger circle is 4 feet larger than the smaller circle. Radius = 24 feet. Circumference = 24 pi.

What was her error?
She should have used 12 in the formula, not 24.
She forgot to multiply the radius by 2 in the formula.
She did not add the additional fence length to the pool’s radius.
She should have used 4 ft in the formula.

Amachine that produces a special type of transistor (a component of computers) has a 2% defective rate. the production is considered a random process where each transistor is independent of the others. (a) what is the probability that the 10th transistor produced is the first with a defect? (b) what is the probability that the machine produces no defective transistors in a batch of 100? (c) on average, how many transistors would you expect to be produced before the first with a defect? what is the standard deviation? (d) another machine that also produces transistors has a 5% defective rate where each transistor is produced independent of the others. on average how many transistors would you expect to be produced with this machine before the first with a defect? what is the standard deviation? (e) based on your answers to parts (c) and (d), how does increasing the probability of an event a↵ect the mean and standard deviation of the wait time until success?