Bài 1:
a) $\frac{x}{12}$ = $\frac{1}{4}$
⇒ $\frac{x}{12}$ = $\frac{3}{12}$
⇒ x = 3
b) $\frac{-5}{x}$ = $\frac{15}{24}$
⇒ $\frac{-5}{x}$ = $\frac{-5}{-8}$
⇒ x = -8
Bài 2:
a) $\frac{4}{9}$ + $\frac{2}{9}$ = $\frac{2+4}{9}$
= $\frac{6}{9}$ = $\frac{2}{3}$
b) $\frac{7}{12}$ - $\frac{14}{21}$ = $\frac{49}{84}$ - $\frac{56}{84}$
= $\frac{49 - 56}{84}$ = $\frac{-1}{12}$
Bài 3:
a) $\frac{1}{6}$ - $\frac{1}{3}$ = $\frac{1}{6}$ - $\frac{2}{6}$
= $\frac{-1}{6}$
c) -4 - $\frac{-1}{4}$
= $\frac{-16}{4}$ - $\frac{-1}{4}$
= $\frac{-15}{4}$
Bài 4:
a) -1.$\frac{9}{12}$ = $\frac{-9}{12}$
= $\frac{-3}{4}$
b) 0 . $\frac{15}{125}$ = 0
Bài 5:
a) x . $\frac{3}{5}$ = $\frac{2}{5}$
⇒ x = $\frac{2}{5}$ : $\frac{3}{5}$
⇒ x = $\frac{2}{3}$
b) $\frac{4}{7}$ : x = $\frac{-1}{8}$
⇒ x = $\frac{4}{7}$ : $\frac{-1}{8}$
⇒ x = $\frac{-32}{7}$
Bài 6:
Ta có:
A = $\frac{9}{14}$ . $\frac{8}{15}$ + $\frac{9}{14}$ . $\frac{7}{15}$ +$\frac{5}{14}$
= $\frac{9}{14}$.($\frac{8}{15}$ + $\frac{7}{15}$)+$\frac{5}{14}$
= $\frac{9}{14}$ . 1 +$\frac{5}{14}$
= $\frac{9}{14}$ +$\frac{5}{14}$
= 1
Đây nhé bạn, nhớ cho ctlhn nha
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