In January, the ratio of the number of students in 6Gr to the number of students in 6Rp was 3:4. In March, 6 students from 6Gr joined 6Rp, the ratio of the number of students in 6Gr to the number of students in 6Rp became 5:9. Find the number of students in 6Gr at first.

Answer 1

Let the number of students in 6Gr in January be 3x.
The number of students in 6Rp in January would be 4x.
In March, after 6 students from 6Gr joined 6Rp, the number of students in 6Gr became 3x - 6, and in 6Rp became 4x + 6.
Accordingly, the ratio of students in 6Gr to the number of students in 6Rp became (3x - 6)/(4x + 6) = 5/9.
Cross-multiplying, we get (3x - 6) * 9 = 5(4x + 6).
Simplifying, we get 27x - 54 = 20x + 30.
Combining like terms, we get 7x = 84.
Dividing both sides by 7, we get x = 12.
Substituting this value back into the expression for the number of students in 6Gr, we get 3x = 3 * 12 = <<3*12=36>>36.
Therefore, the number of students in 6Gr at first was 36. Answer: \boxed{36}.