Answer:
Q3 represents 75%, meaning a z of ~0.67
80 - 70 is 10, so the standard deviations is ~14.9.
10 / 0.67 = 14.9
now find the z that represents a score of 90
90 - 70 is 20
20 / 14.9 = 1.34
from a z-table, a z of 1.34 represents a probability of ~90.99% meaning that there is about a 9.01% chance of getting a 90 or better.
