Đáp án:

 

Giải thích các bước giải:

Bài 1:

a) $\frac{6}{7}$ + $\frac{5}{8}$ x $\frac{1}{5}$ - $\frac{3}{16}$ x 4

= $\frac{6}{7}$ + $\frac{5.8}{1.5}$ - $\frac{3.4}{16}$ 

= $\frac{6}{7}$ + $\frac{40}{5}$ - $\frac{12}{16}$

= $\frac{6}{7}$ + 8 - $\frac{3}{4}$

= $\frac{6}{7}$ + $\frac{56}{7}$ - $\frac{3}{4}$

= $\frac{62}{7}$ - $\frac{3}{4}$

= $\frac{248}{28}$ - $\frac{21}{28}$

= $\frac{227}{28}$

b) $\frac{-1}{6}$ + $\frac{2}{3}$ x ($\frac{-3}{4}$) + $\frac{4}{5}$

= $\frac{-1}{6}$ + $\frac{-6}{12}$ + $\frac{4}{5}$

= $\frac{-1}{6}$ + $\frac{-3}{6}$ + $\frac{4}{5}$

= $\frac{-4}{6}$ + $\frac{4}{5}$

= $\frac{-2}{3}$ + $\frac{4}{5}$

= $\frac{-10}{15}$ + $\frac{12}{15}$

= $\frac{2}{15}$

Bài 2:

a) x - $\frac{6}{7}$ + $\frac{1}{4}$ = 3

x - $\frac{6}{7}$ = 3 - $\frac{1}{4}$

x - $\frac{6}{7}$ =  $\frac{12}{4}$ - $\frac{1}{4}$

x - $\frac{6}{7}$ =  $\frac{11}{4}$

x = $\frac{11}{4}$ + $\frac{6}{7}$

x = $\frac{77}{28}$ + $\frac{24}{28}$

x = $\frac{101}{28}$

b) x - 7 + $\frac{4}{6}$ = $\frac{-1}{5}$

x - 7 = $\frac{-1}{5}$ - $\frac{4}{6}$

x - 7 = $\frac{-6}{30}$ - $\frac{20}{30}$

x - 7 = $\frac{-26}{30}$ = $\frac{-13}{15}$

x = $\frac{-13}{15}$ + 7

x = $\frac{-13}{15}$ + $\frac{105}{15}$

x = $\frac{92}{15}$

Bài 3

a) $\frac{-1}{3}$ x $\frac{7}{24}$ : $\frac{14}{36}$

= $\frac{-7}{72}$ . $\frac{36}{14}$

= $\frac{-7}{72}$ . $\frac{7}{18}$

= $\frac{-49}{1296}$

b) $\frac{5}{4}$ - $\frac{1}{2}$ + $\frac{-7}{8}$

= $\frac{10}{8}$ - $\frac{4}{8}$ - $\frac{7}{8}$

= $\frac{-1}{8}$