Question

The SAT scores are normally distributed with a mean of 1019 and a standard deviation of 90. If a university accepts only the students who scores at top 10% on SAT, what is the cutoff score?

Answer 1

Do you understand the Z-score corresponding to the 90th percentile of a Normal Distribution?

Answer 2

no

Answer 3

This gives something of a clear explanation of Z-Scores:
https://statistics.laerd.com/statistical-guides/standard-score.php
Essentially, there is a point in a Normal distribution where 90% of the data will fall to the left and 10% will fall to the right. Z-score puts this point in terms of the "number of standard deviations above the mean".