Bài 1:Tính hợp lý
a) A= $\frac {-5}{11}$ + 75% -1$\frac{1}{2}$ -$\frac{1}{4}$ +$\frac{6}{-11}$
b)B= $\frac{19-19.5}{19.2-76}$
c)C= $\frac{-7}{11}$. $\frac{4}{13}$+ $\frac{7}{11}$. $\frac{-9}{13}$+ $\frac{6}{11}$
d) D= 7 $\frac{5}{11}$ – (5$\frac{5}{8}$-4 $\frac{6}{11}$ )
Bài 2 Tìm x , biết
a) $\frac{3}{7}$ x – $\frac{3}{4}$= $\frac{1}{2}$
b) $\frac{7}{12}$- 2$\frac{1}{2}$ : x =$\frac{-5}{12}$
c) x : ($\frac{3}{8}$ – $\frac{3}{4}$ )= -3$\frac{1}{2}$
d) (2x+ $\frac{3}{4}$ ) ( $\frac{5}{7}$ – 3x)= 0
Đáp án:
Bài 1
a)$\frac{-3}{2}$
b) 2
c) $\frac{-1}{11}$
d)$\frac{51}{8}$
Bài 2
a) $\frac{35}{12}$
b) $\frac{5}{2}$
c) $\frac{21}{16}$
d) $\frac{-5}{21}$
Giải thích các bước giải:
Bài 1
A = $\frac{-5}{11}$+ 75% -1 $\frac{1}{2}$ + $\frac{1}{4}$ + $\frac{6}{-11}$
= ($\frac{-5}{11}$ + $\frac{-6}{11}$) +($\frac{3}{4}$+$\frac{1}{4}$) +$\frac{-3}{2}$
=$\frac{-11}{11}$ +1 +$\frac{-3}{2}$
= -1 +1 +$\frac{-3}{2}$
= $\frac{-3}{2}$
b) B = $\frac{19 -19.5}{19.2-76}$
=$\frac{19 .1- 19. 5}{19.2-19.24}$
=$\frac{19 .(1-5)}{19.(2-4)}$
=$\frac{19 -(-4)}{19.(-2)}$
= 2
c)C= $\frac{-7}{11}$. $\frac{4}{13}$+ $\frac{7}{11}$. $\frac{-9}{13}$+ $\frac{6}{11}$
=$\frac{-7}{11}$. ($\frac{4}{13}$+ $\frac{9}{13}$) $\frac{6}{11}$
= $\frac{-7}{11}$ . 1 + $\frac{6}{11}$
= $\frac{-1}{11}$
d) D= 7 $\frac{5}{11}$ – (5$\frac{5}{8}$-4 $\frac{6}{11}$ )
= 7 $\frac{5}{11}$ – 5$\frac{5}{8}$+4 $\frac{6}{11}$
= (7$\frac{5}{11}$ +4$\frac{6}{11}$ ) – 5$\frac{5}{8}$
= 12 – 5 – $\frac{5}{8}$
= 7 – $\frac{5}{8}$
= $\frac{51}{8}$
Bài 2 Tìm x , biết
a) $\frac{3}{7}$ x – $\frac{3}{4}$= $\frac{1}{2}$
$\frac{3}{7}$ x = $\frac{1}{2}$ + $\frac{3}{4}$
$\frac{3}{7}$ x = $\frac{5}{4}$
x = $\frac{5}{4}$ : $\frac{3}{7}$
x= $\frac{35}{12}$
b) $\frac{7}{12}$- 2$\frac{1}{2}$ : x =$\frac{-5}{12}$
$\frac{5}{2}$ : x = $\frac{7}{12}$ – $\frac{-5}{12}$
x =$\frac{5}{12}$ : 1
x= $\frac{5}{2}$
c) x : ($\frac{3}{8}$ – $\frac{3}{4}$ )= -3$\frac{1}{2}$
x : $\frac{-3}{8}$ = $\frac{-7}{2}$
x = $\frac{-7}{2}$ . $\frac{-3}{8}$
= $\frac{21}{16}$
d) (2x+ $\frac{3}{4}$ ) ( $\frac{5}{7}$ – 3x)= 0
2x + $\frac{3}{4}$ = 0 hoặc $\frac{5}{7}$ – 3x = 0
2x = $\frac{-3}{4}$
x = $\frac{-3}{4}$ : 2
x = $\frac{-3}{8}$
—————————-
$\frac{5}{7}$ – 3x = 0
3x = $\frac{-5}{7}$
x= $\frac{-5}{7}$ : 3
x = $\frac{-5}{21}$
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@Lichaeng