(2) Number of students in school B = 1200× 150 360 = 500, and number of students in school C = 1200× 90 360 = 300.

∴D Total population = 400× 36.25%+500× 57.6%+300× 38% = 547,

The percentage of students whose answers are completely correct is m = 547 1200 ≈ 45.58%.

(3) A large proportion of students in C school make calculation errors, so teachers in C school should strengthen the application and mastery of calculation.