C1 : Lê Quốc Trần Anh and Đào Trọng Luân

C2:

There are : 100% - 25% = 75% (students) are good students

There are all good students : 900 . 75% = 675 (students) are good students

There are: \(900.25\%=225\left(students\right)\)are weak students

So there are: \(900-225=675\left(students\right)\) are good students

675

hk tốt

There are 100% - 25% = 75% are good students

So there are 900.75%=675 ( students ) are good students 

There are 100% - 25% = 75 % good students

So there are 900 . 75% = 675 ( students ) are good students

There are \(900\cdot25\%=225\) weak students

So there are: 900 - 225 = 675 good students

So.................