All applicants for a job in X-Company should take a test. To be invited for an interview your score on the test should be on the top P percent of all applicants. Results of the test have Normal Distribution with the mean M and Standard Deviation SD.
Take values M, SD and P and
1. From Appendix Table for Normal Distribution find z-value that has area to the left close to 1-P (P should be in decimal form).
2. In formula z=(x-M)/SD to plug your z, M and SD and solve for x. That will be score on the test required to be invited for the interview.
M=200, SD=50, P=20%