Đáp án:
Bài 1 :
1. Ta có :
$\dfrac{13}{16}$ . $\dfrac{-29}{30}$ - $\dfrac{29}{30}$ .$\dfrac{27}{16}$ + $\dfrac{3}{16}$
=$\dfrac{-13}{16}$ . $\dfrac{29}{30}$ - $\dfrac{29}{30}$ .$\dfrac{27}{16}$ + $\dfrac{3}{16}$
= $\dfrac{29}{30}$ . ( $\dfrac{-13}{16}$ - $\dfrac{27}{16}$) + $\dfrac{3}{16}$
= $\dfrac{29}{30}$ . $\dfrac{-40}{16}$ + $\dfrac{3}{16}$
= $\dfrac{-58}{24}$ + $\dfrac{3}{16}$
= $\dfrac{-116}{48}$ + $\dfrac{9}{48}$
= $\dfrac{-107}{48}$
2. Ta có :
$ 1,25 . 2,5 . (-8) . (-4)$
$ =[1,25 . (-8)].[2,5 . (-4)]$
$ = (-10).(- 10) = 100$
Câu3
1. Ta có :
$\dfrac{2}{3}$ . x - $\dfrac{4}{5}$ = $\dfrac{3}{4}$
<=> $\dfrac{2}{3}$ . x = $\dfrac{3}{4}$ + $\dfrac{4}{5}$
<=> $\dfrac{2}{3}$ . x = $\dfrac{31}{20}$
<=> x = $\dfrac{31}{20}$ : $\dfrac{2}{3}$
<=> x = $\dfrac{93}{40}$
2. Ta có :
$(3x - 18) : 15 = -4$
$ <=> 3x - 18 = -60$
$ <=> 3x = -60 + 18$
$ <=> 3x = -42$
$ <=> x = -14$
3. Ta có :
$\dfrac{-5}{6}$ - $\dfrac{1}{6}$ : x = $\dfrac{5}{12}$
<=> $\dfrac{1}{6}$ : x = $\dfrac{-5}{6}$ - $\dfrac{5}{12}$
<=> $\dfrac{1}{6}$ : x = $\dfrac{-5}{4}$
<=> x = $\dfrac{1}{6}$ : $\dfrac{-5}{4}$
<=> x = $\dfrac{-2}{15}$
4. Ta có :
( $\dfrac{7}{8}$ - x ). $\dfrac{2}{3}$ = 4
<=> $\dfrac{7}{8}$ - x = 4 : $\dfrac{2}{3}$
<=> $\dfrac{7}{8}$ - x = 6
<=> x = $\dfrac{7}{8}$ - 6
<=> x = $\dfrac{-41}{8}$
Giải thích các bước giải:
