Đáp án:
Giải thích các bước giải:
`A=(1.98+2.97+...+98.1)/(1.2+2.3+...+98.99`
`=>A/3=((1+2+...+98).(1+2+...+98))/(1.2.3+2.3.3+...+98.99.3`
`=>`$\dfrac A3=\dfrac{\left(\dfrac{98.99}{2}\right).\left(\dfrac{98.99}{2}\right)}{1.2.3+2.3.(4-1)\,+\,.\!.\!.+98.99.(100-97)}\\\Rightarrow \dfrac A3=\dfrac{4851.4851}{1.2.3+2.3.4-1.2.3\,+\,.\!.\!.+98.99.100-97.98.99}\\\Rightarrow \dfrac A3=\dfrac{4951^2}{98.99.100}\\\Rightarrow A=\dfrac{4951^2}{33.98.100}\\\Rightarrow A=\dfrac{24512401}{323400}$
