1.
2.
a) $\frac{11}{2}$ = $\frac{11x5}{2x5}$ = $\frac{55}{10}$
b) $\frac{15}{4}$ = $\frac{15x25}{4x25}$ = $\frac{375}{100}$
c) $\frac{31}{5}$ = $\frac{31x2}{5x2}$ = $\frac{62}{10}$
d) $\frac{18}{125}$ = $\frac{18x8}{125x8}$ = $\frac{144}{1000}$
3.
a) $\frac{6}{25}$ = $\frac{6x4}{25x4}$ = $\frac{24}{100}$
b) $\frac{500}{1000}$ = $\frac{500:10}{1000:10}$ = $\frac{50}{100}$
c) $\frac{18}{200}$ = $\frac{18:2}{200:2}$ = $\frac{9}{100}$
d) $\frac{72}{600}$ = $\frac{72:6}{600:6}$ = $\frac{12}{100}$
e) $\frac{75}{625}$ = $\frac{75:25x4}{625:25x4}$ = $\frac{12}{100}$
4.
Đáp án: B.