What fraction of all students received 90% or higher?
9/10 of the class received 70% or higher. of the students receving 70% or higher, 1/4 received 90% or higher. What fraction of all students received 90% or higher?
90% received a 70% or higher, and 25% of those received a 90% or higher
0.9 * 0.25 = 0.225
22.5% of the class received 90% or higher