There were a certain number of students in both Class A and Class B. After 10% of the students in Class A were transferred into Class B, the number of students in Class B was increased by 20%. If there are 30 students in Class B now, how many students were originally in Class A?
For Class B
The number of students was increased by 20% to 30, then its original number of students is 100% and the final number is 100% + 20% = 120%.
Use the formula: Whole = Part ÷ Percent
The original number of students in Class B: 30 ÷ 120% = 25
Thus, the transferred students: 30 25 = 5
For Class A,
10% of its original students is 5.
Thus, the original number of students in Class A: 5 ÷ 10% = 50