Đáp án :
`(1.5.6+2.10.12+3.15.18+4.20.24+5.25.30)/(13.5+2.6.10+3.9.15+4.12.20+5.15.25)`
`= (1.5.6+1.2.5.2.6.+1.3.5.3.6.3+1.4.5.4.6.4+1.5.5.5.6.5)/(1.3.5+1.2.3.2.5.2+1.3.3.3.5.3+1.4.3.4.5.4+1.5.3.5.5.5)`
`=((1.5.6).(1+2+3+4+5))/((1.3.5).(1+2+3+4+5) `
`= ((1.5.6).\cancel((1+2+3+4+5)))/((1.3.5).\cancel((1+2+3+4+5)))`
`= (1.5.6)/(1.3.5) = 2 `
`Go od luck!`