Giai
Goi x la so hoc sinh cua truong do
Theo de bai: x chia het cho 10, 12, 15 va x < 400
Vay x \(\in\) BC(10; 12; 15) va x < 400
10 = 2 . 5
12 = 22 . 3
15 = 3 . 5
Thua so nguyen to chung, rieng: 2; 3; 5
BCNN(10; 12; 15) = 22 . 3 . 5 = 60
BC(10; 12; 15) = B(60) = {0; 60; 120; 180; 240; 300; 360; 420; ...}
Vi: x < 400
Nen: x = 60; 120; 180; 240; 300; 360
Vay so hoc sinh cua truong do la 60; 120; 180; 240; 300; 360 ( hoc sinh )