Sửa đề

a) 37.24 + 37.76 + 63.79 + 21.63

= 37.(24 + 76) + 63.(79 + 21)

= 37.100 + 63.100

= 100.(37 + 63)

= 100.100

= 10000

b) 49 + (139 - 172 + 99) - (139 + 199 - 172)

= 49 + 139 - 172 + 99 - 139 - 199 + 172

= 49 + (139 - 139) + (172 - 172) + (99 - 199)

= 49 + 0 + 0 - 100

= -51

13: \(\left(-15\right)+8+7\)

\(=\left(-15\right)+\left(8+7\right)\)

=-15+15

=0

14: \(\left(-8\right)+2+6\)

\(=\left(-8\right)+\left(2+6\right)\)

=-8+8

=0

15: \(\left(-1\right)+3-2\)

\(=\left(-1-2\right)+3\)

=-3+3

=0

16: \(25-8-7\)

\(=25-\left(8+7\right)\)

=25-15

=10

17: \(8-2-6\)

\(=8-\left(2+6\right)\)

=8-8

=0

18: \(\left(-12\right)-3+15\)

\(=\left(-12-3\right)+15\)

=-15+15

=0

ra 180

= -65.18+65.75-75.65+75.18

=18.(-65+75)

8)3

9)6

10)23/7

\(8)\) \(( -6,2 :2 + 3,7 ) : 0,2 = ( -3,1 + 3,7 ) : 0,2 = 0,6 : 0,2 = 3\)

\(9) \) \( 4 \dfrac{11}{23} - \dfrac{9}{14} + 2 \dfrac{12}{23} - \dfrac{5}{14}\)

\(= ( 4 \dfrac{11}{23} + 2 \dfrac{12}{23}) - ( \dfrac{5}{14} + \dfrac{9}{14} )\)

\(= 8- \dfrac{14}{14} \)

\(= 8-1\)

\(=7\)

\(10)\) \(11 \dfrac{1}{4} - ( 2 \dfrac{5}{7} + 5\dfrac{1}{4} )\)

\(= 11 \dfrac{1}{4} - 2 \dfrac{5}{7} - 5\dfrac{1}{4} \)

\(= 11 \dfrac{1}{4} - 5\dfrac{1}{4} - 2 \dfrac{5}{7}\)

\(= 6 - \dfrac{19}{7} = \dfrac{42}{7} - \dfrac{19}{7} = \dfrac{23}{7}\)

Lời giải:

$=\frac{81}{20}.\frac{4}{9}+\frac{4}{15}: \frac{-4}{7}$

$=\frac{9.9.4}{4.5.9}+\frac{4}{15}.\frac{-7}{4}$

$=\frac{9}{5}+\frac{-7}{15}=\frac{27}{15}+\frac{-7}{15}=\frac{20}{15}=\frac{4}{3}$

\(\dfrac{50-\dfrac{6}{13}+\dfrac{3}{19}-\dfrac{3}{23}}{100-\dfrac{12}{13}+\dfrac{6}{19}-\dfrac{6}{23}}\)

\(=\dfrac{50-\dfrac{6}{13}+\dfrac{3}{19}-\dfrac{3}{23}}{2\left(50-\dfrac{6}{13}+\dfrac{3}{19}-\dfrac{3}{23}\right)}\)

\(=\dfrac{1}{2}\)

31: (-29)+8-9

\(=\left(-29\right)+\left(8-9\right)\)

\(=-29-1=-30\)

32: \(\left(-14\right)-6-10\)

\(=\left(-14-6\right)-10\)

=-20-10

=-30

33: \(\left(-42\right)+10+2\)

\(=\left(-42\right)+\left(10+2\right)\)

=-42+12

=-30

34: \(\left(-45\right)+25-20\)

\(=\left(-45\right)+\left(25-20\right)\)

=-45+5

=-40

35: \(\left(-60\right)+17+3\)

\(=\left(-60\right)+\left(17+3\right)\)

=-60+20

=-40

36: \(\left(-48\right)+18-10\)

\(=\left(-48+18\right)-10\)

=-30-10

=-40

câu d) 

\(\dfrac{6}{5}+\left(3+\dfrac{-1}{5}\right)\\ =\dfrac{6}{5}+3+\dfrac{-1}{5}\\ =1+3=4\)

câu e)

\(-\dfrac{3}{5}+\left(-\dfrac{2}{5}+2\right)\\ =\dfrac{-3}{5}+\dfrac{-2}{5}+2\\ =-1+2=1\)

câu f)

\(\dfrac{8}{3}-\left(-\dfrac{4}{3}+3\right)\\ =\dfrac{8}{3}+\dfrac{4}{3}-3\\ =4-3=1\)