We were told that the school admissions office accepts 2 out of every 7 applicants. Thus, the probability that the school accepts an applicant is 2/7
There are only two outcomes. It is either the school accepts an applicant or it doesn't. If the school accepts 630 students, It means that 2/7 of the total number of applicants were accepted
Assuming the totla number of applicants is x, it means that
2/7 * x = 630
2x = 630 * 7 = 4410
x = 4410/2
x = 2205
The total number of applicants is 2205
The number of applicants that were not accepted is
2205 - 630 = 1575
1575 applicants were not accepted
