Question

Rút gọn các phân số sau:

\(\dfrac{13.11-13}{13.15}\);

\(\dfrac{1989.1990+3978}{1992.1991-3984}\)

Answer 1

\(\dfrac{13.11-13}{13.15}=\dfrac{13.11-13.1}{13.15}=\dfrac{13.\left(11-1\right)}{13.15}=\dfrac{13.10}{13.15}=\dfrac{1.2}{1.3}=\dfrac{2}{3}\)

\(\dfrac{1989.1990+3978}{1992.1991-3984}=\dfrac{1989.1990+2.1989}{1992.1991-2.1992}=\dfrac{1989.\left(1990+2\right)}{1992.\left(1991-2\right)}=\dfrac{1989.1992}{1992.1989}=\dfrac{1.1}{1.1}=1\)

Answer 2

Lời giải:

a, \(\dfrac{13.11-13}{13.15}=\dfrac{13.\left(11-1\right)}{13.15}=\dfrac{13.10}{13.15}=\dfrac{2}{3}\)

b, \(\dfrac{1989.1990+3978}{1992.1991-3984}=\dfrac{1989.1990+1989.2}{1992.1991-1992.2}=\dfrac{1989.\left(1990+2\right)}{1992.\left(1991-2\right)}=\dfrac{1989.1992}{1992.1989}=1\)