There are 42 students in a class.
Each student walks to school or cycles to school or gets the bus to school.
There are 23 girls in the class.
10 of the girls walk to school.
6 of the boys cycle to school.
7 of the 11 students who get the bus to school are boys.
Find the number of these students who walk to school.
Your final line must say, Number who walk to school = ...

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?