1.
a) $\frac{7}{9}$ + $\frac{9}{10}$ = $\frac{7x10}{9x10}$ + $\frac{9x9}{10x9}$ = $\frac{151}{90}$
b) $\frac{5}{6}$ + $\frac{7}{8}$ = $\frac{5x4}{6x4}$ + $\frac{7x3}{8x3}$ = $\frac{41}{24}$
2.
a) $\frac{5}{8}$ - $\frac{2}{5}$ = $\frac{5x5}{8x5}$ - $\frac{2x8}{5x8}$ = $\frac{9}{40}$
b) 1 $\frac{1}{10}$ - $\frac{3}{4}$ = $\frac{11}{10}$ - $\frac{3}{4}$ = $\frac{7}{20}$
3.
9m 5dm = 9m + $\frac{5}{10}$ m = 9 $\frac{5}{10}$ m
8m 9cm = 8m + $\frac{9}{100}$ m = 8 $\frac{9}{100}$ m
12cm 5mm = 12 cm + $\frac{5}{10}$ m = 12 $\frac{5}{10}$ m
4.
Bài giải
Quãng đường AB dài số ki-lô-mét là:
12 : $\frac{3}{10}$ = 40 (km)
Đáp số: 40 km.
5.
a) $\frac{11}{15}$ - $\frac{3}{5}$ = $\frac{2}{15}$
b) $\frac{35}{14}$ - $\frac{1}{2}$ = 2