Goi so hoc sinh cua truong THCS la a (a∈N*/ don vi : em/1000≤a≤1100)
vi a chia het cho ca 15,18 va 24 nen
=>a∈BC(15,18,24)
TC:15=3.5 18=2.3² 24=2³ .3
BCNN(15,18,24)=2³.3².5=360
=>BC(15,18,24)=B(360)=(0,360,720,1080,1440,....}
Do 1000≤a≤1100 nen
=> a =1080
Vay : Truong THCS do co 1080 em HS