tính bằng cách thuận tiên nhất :

`a,213 + 367 - 267 - 33`

`=213 +  (367 - 267)-33`

`=213 + 100 -33`

`= 313-33`

`=280`

`b,15 - 14 + 13 - 12 + 11 - 10 + 9 - 8`

`=(15-14)+(13-12)+(11-10)+(9-8)`

`= 1 + 1 + 1 +1`

`= 2+2`

`=4`

a, 213 + 367 - 267 - 33

= (213 - 33) + (367 - 267)

= 180 + 100

= 280

b, 15 - 14 + 13 - 12 + 11 - 10 + 9 - 8

= (15 - 14) (9 - 8)

= 1 + 1 + 1 + 1

= 4

(19+1)+(18+2)+(17+3)+(16+4)+(15+5)+(14+6)+(13+7)+(12+8)+(11+9)+20)+10

=20+20+20+20+20+20+20+20+20+20=(20*10)+10

=210

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20

=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+(10+20)

=20+20+20+20+20+20+20+20+20+30

=(20 x 9) + 30

=180 + 30

=210

tk nha

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20

= (1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+20+10

= 20     +   20   +  20     +  20    +  20      +  20    +  20     +  20    +  20     +  20 + 10

= 10 . 10 +10 

=  100     +  10 = 110

1) Ta có: \(\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{7}{25}\cdot\dfrac{5}{7}\right)\)

\(=\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{1}{5}\right)\)

=0

2) Ta có: \(\dfrac{8}{17}\cdot\dfrac{4}{15}+\dfrac{8}{17}\cdot\dfrac{22}{15}-\dfrac{8}{15}\cdot\dfrac{9}{17}\)

\(=\dfrac{8}{17}\left(\dfrac{4}{15}+\dfrac{22}{15}-\dfrac{9}{15}\right)\)

\(=\dfrac{8}{17}\cdot\dfrac{15}{15}=\dfrac{8}{17}\)

3) Ta có: \(\dfrac{2021}{2}\cdot\dfrac{1}{3}+\dfrac{4042}{4}\cdot\dfrac{1}{5}+\dfrac{6063}{3}\cdot\dfrac{22}{15}\)

\(=\dfrac{2021}{2}\left(\dfrac{1}{3}+\dfrac{1}{5}\right)+2021\cdot\dfrac{22}{15}\)

\(=\dfrac{2021}{2}\cdot\dfrac{8}{15}+\dfrac{2021}{2}\cdot\dfrac{44}{15}\)

\(=\dfrac{2021}{2}\cdot\dfrac{52}{15}\)

\(=\dfrac{52546}{15}\)

4) Ta có: \(\dfrac{4}{7}\cdot\dfrac{2}{13}+\dfrac{8}{13}:\dfrac{7}{4}+\dfrac{4}{7}:\dfrac{13}{2}+\dfrac{4}{7}\cdot\dfrac{1}{13}\)

\(=\dfrac{4}{7}\left(\dfrac{2}{13}+\dfrac{8}{13}+\dfrac{2}{13}+\dfrac{1}{13}\right)\)

\(=\dfrac{4}{7}\)

1) Tính biểu thức:

nhiều thế

sfdhg 

a) \(\dfrac{5}{9}+\dfrac{13}{7}+\dfrac{15}{13}+\dfrac{8}{7}+\dfrac{4}{9}+\dfrac{11}{13}\)

\(=\left(\dfrac{5}{9}+\dfrac{4}{9}\right)+\left(\dfrac{13}{7}+\dfrac{8}{7}\right)+\left(\dfrac{15}{13}+\dfrac{11}{13}\right)\)

\(=1+3+2\)

\(=6\)

b) \(\dfrac{3}{5}+\dfrac{18}{9}+\dfrac{4}{10}\)

\(=0,6+2+0,4\)

\(=\left(0,6+0,4\right)+2\)

\(=1+2\)

\(=3\)

\(a\dfrac{5}{9}+\dfrac{4}{9}+\dfrac{13}{7}+\dfrac{8}{7}+\dfrac{15}{13}+\dfrac{11}{13}=\dfrac{9}{9}+\dfrac{21}{7}+\dfrac{26}{13}=1+3+2=6\)

\(b\dfrac{3}{5}+2+\dfrac{2}{5}=\dfrac{5}{5}+2=1+2=3\)

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20

=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+20+10

=20+20+20+20+20+20+20+20+20+20+10

=20×10+10

=200+10

=210

= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) + (4 + 16 ) + ( 5 + 15 ) + ( 6 + 14 ) + ( 7 + 13 ) + ( 8 + 12) + ( 9+ 11 ) + 20

= 20 + 20 + 20 +20 +  20 +20 + 20 + 20 + 20 +20

= 20 x 10

= 200

tui đầu tiên đó 

Ta có : \(1+2+3+...+19+20\)

          \(=\frac{\left(20+1\right).20}{2}=\frac{21.20}{2}=210\)

( 6 x 8 – 48) : ( 10 + 11 + 12 + 13 + 14 + 15 )

= (48 – 48) : ( 10 + 11 + 12 + 13 + 14 + 15 )

= 0 : ( 10 + 11 + 12 + 13 + 14 + 15 )

= 0

câu trả lời là 0

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a.      ( 6 x 8 – 48 ) : ( 10 + 11 + 12 + 13 + 14 + 15 )

= (48 – 48) : ( 10 + 11 + 12 + 13 + 14 + 15 )

= 0 : ( 10 + 11 + 12 + 13 + 14 + 15 )

= 0