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?

students

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