72 is 80 percent of 90.
22% of 80 students is 17.6 students.
20 percent of 645 is 129.
20 of them
30% of 645 is 193.5
80 x 0.1 = 8 students
22% means 22/100 = 0.22 0.22 * 80 = 17.6 students ( call it 18 )
645
41.92
80%
80, remainder 5
80 = 100% 8 = 10% 32 = 40% 80 - 32 = 48