a) 3h 20ph = 3 và 1/3 = 10/3

b) 1h 45 ph = 1 và 3/4 = 7/4

c) 2h 40 ph = 2 và 2/3 = 8/3

Bài 4:

a; \(\dfrac{1}{4}\) - \(\dfrac{1}{5}\) = \(\dfrac{5}{20}\) - \(\dfrac{4}{20}\) = \(\dfrac{1}{20}\)

b; \(\dfrac{3}{5}\) - \(\dfrac{-1}{2}\) = \(\dfrac{6}{10}\) + \(\dfrac{5}{10}\) = \(\dfrac{11}{10}\)

c; \(\dfrac{3}{5}\) - \(\dfrac{-1}{3}\) = \(\dfrac{9}{15}\) + \(\dfrac{5}{15}\) = \(\dfrac{14}{15}\)

d; \(\dfrac{-5}{7}\) - \(\dfrac{1}{3}\)= \(\dfrac{-15}{21}\) - \(\dfrac{7}{21}\)= \(\dfrac{-22}{21}\)

Bài 5

a; 1 + \(\dfrac{3}{4}\) = \(\dfrac{4}{4}\) + \(\dfrac{3}{4}\) = \(\dfrac{7}{4}\)       b; 1 - \(\dfrac{1}{2}\) = \(\dfrac{2}{2}\) - \(\dfrac{1}{2}\) = \(\dfrac{1}{2}\)

c; \(\dfrac{1}{5}\) - 2 = \(\dfrac{1}{5}\) - \(\dfrac{10}{5}\) = \(\dfrac{-9}{5}\)     d; -5 - \(\dfrac{1}{6}\) = \(\dfrac{-30}{6}\) - \(\dfrac{1}{6}\) = \(\dfrac{-31}{6}\)

e; - 3 - \(\dfrac{2}{7}\)= \(\dfrac{-21}{7}\) - \(\dfrac{2}{7}\)= \(\dfrac{-23}{7}\)     f; - 3 + \(\dfrac{2}{5}\) = \(\dfrac{-15}{5}\) + \(\dfrac{2}{5}\)= - \(\dfrac{13}{5}\)

g; - 3 - \(\dfrac{2}{3}\) = \(\dfrac{-9}{3}\) - \(\dfrac{2}{3}\) = \(\dfrac{-11}{3}\)     h; - 4 - \(\dfrac{-5}{7}\) = \(\dfrac{-28}{7}\)+ \(\dfrac{5}{7}\) = - \(\dfrac{23}{7}\)

Bài 2: 

\(\dfrac{12}{-24}=\dfrac{12:12}{-24:12}=\dfrac{1}{-2}\)

\(\dfrac{-39}{75}=\dfrac{-39:3}{75:3}=\dfrac{-13}{25}\)

\(\dfrac{132}{-264}=\dfrac{132:132}{-264:132}=\dfrac{1}{-2}\)

Bài 3:

\(\dfrac{1}{-2}=\dfrac{-1}{2};\dfrac{-3}{-5}=\dfrac{3}{5};\dfrac{2}{-7}=\dfrac{-2}{7}\)

Bài 4:

\(15p=\dfrac{1}{4}h;20p=\dfrac{1}{3}h;45p=\dfrac{3}{4}h;50p=\dfrac{5}{6}h\)

2. Các cặp số đối với nhau là:

\(\dfrac{-5}{6}\) và \(\dfrac{5}{6}\)

\(\dfrac{-40}{-10}\) và \(\dfrac{40}{-10}\)

BÀi 1: 

\(\dfrac{\overline{abab}}{\overline{cdcd}}\) = \(\dfrac{\overline{abab:}101}{\overline{cdcd}:101}\) = \(\dfrac{\overline{ab}}{cd}\) 

\(\dfrac{\overline{abcabc}}{\overline{abc}}\) = \(\dfrac{\overline{abc}\times1001}{\overline{abc}}\) = 1001

Có quá nhiều bài, thứ nhất em đăng tách ra, thứ hai chụp gần cận cho rõ, thứ ba em chỉ đăng bài cần giúp

Bài 3:

a; \(\frac56-\frac89\) = \(\frac{15}{18}-\) \(\frac{16}{18}\) = - \(\frac{1}{18}\)

d; \(\frac{5}{16}-\frac{5}{24}\)

= \(\frac{15}{48}\) - \(\frac{10}{48}\)

= \(\frac{5}{48}\)

e; - \(\frac{7}{30}\) + \(\frac{8}{45}\)

= \(-\frac{21}{90}\) + \(\frac{16}{90}\)

= - \(\frac{5}{90}\)

= - \(\frac{1}{18}\)

f; \(\frac{7}{12}-\frac{-9}{20}\)

= \(\frac{35}{60}\) + \(\frac{27}{60}\)

= \(\frac{62}{60}\)

= 31/30

h; - \(\frac48\) + \(-\frac{3}{10}\)

= -\(\frac{20}{40}-\frac{12}{40}\)

= - \(\frac{32}{40}\)

= - \(\frac45\)