Question

1- Scores on a certain math test are normally distributed with a mean of 68, and a standard deviation of 15.
The instructor decides to set the grade cut-off points such that the top 20% of the students will get an A, the next 30% will get a B.
What will be the cut-off scores for A and for B?
Cut-off score for 'A' is:  (Give 1 decimal place)
Cut-off score for 'B' is:

2- Spray drift is a constant concern for pesticide applicators and agricultural producers. The inverse relationship between droplet size and drift potential is well known. The paper "Effects of 2,4-D Formulation and Quinclorac on Spray Droplet Size and Deposition"† investigated the effects of herbicide formulation on spray atomization. A figure in a paper suggested the normal distribution with mean 1050 µm and standard deviation 150 µm was a reasonable model for droplet size for water (the "control treatment") sprayed through a 760 ml/min nozzle.

(a) What is the probability that the size of a single droplet is less than 1470 µm? At least 925 µm? (Round your answers to four decimal places.)

less than 1470 µm
at least 925 µm

(b) What is the probability that the size of a single droplet is between 925 and 1470 µm? (Round your answer to four decimal places.)

Answer 1