Đặt `A=(1xx3xx5+2xx6xx10+4xx12xx20+7xx21xx35)/(1xx5xx7+2xx10xx14+4xx20xx28+7xx35xx49)`
`A=(15+120+960+5145)/(35+280+2240+12005)`
`A=((15+5145)+(960+120))/((35+12005)+(280+2240))`
`A=(5160+1080)/(12040+2520)`
`A=6240/14560`
`A=39/91=3/7`
Ta so sánh `3/7` và `303/708` :
Ta có : `303/708=(303:3)/(708:3)=101/236`
`3/7=(3xx236)/(7xx236)=708/1652`
`101/236=(101xx7)/(236xx7)=707/1652`
Mà `708/1652>707/1652` nên `A>303/708`