\(\dfrac{3}{5}+\dfrac{6}{11}+\dfrac{7}{13}+\dfrac{2}{5}+\dfrac{16}{11}+\dfrac{19}{13}\\ =\left(\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(\dfrac{6}{11}+\dfrac{16}{11}\right)+\left(\dfrac{7}{13}+\dfrac{19}{13}\right)\\ =\dfrac{5}{5}+\dfrac{22}{11}+\dfrac{26}{13}\\ =1+2+2\\ =5\)

5

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 : \(1+2+3+...+19+20\)

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

\(\frac{3}{5}+\frac{6}{11}+\frac{7}{13}+\frac{2}{5}+\frac{16}{11}+\frac{19}{13}\)

\(=\left(\frac{3}{5}+\frac{2}{5}\right)+\left(\frac{6}{11}\frac{16}{11}\right)+\left(\frac{7}{13}+\frac{19}{13}\right)\)

\(=1+2+2\)

\(=5\)

a

        [3/5+2/5]+[7/13+19/13]+[6/11+16/11]=5

a. 3/5 + 6/11 + 7/13 + 2/5 + 16/11 + 19/13

 = ( 3/5 + 2/5 ) + ( 6/11 + 16/11 ) + ( 7/13 + 19/13)

 = 1 + 2 + 2

 = 5.

de om 5 chu may

vì 5/5+22/11+26/13=1+2+2=5

(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

a)   17/23+(1-17/23)

=17/23+1-17/23

=1

b)17/12+9/7-(2/7+5/12)

=17/12+9/7-2/7-5/12

=1+1

=2

c)

7/13-(4/7-6/13)

=7/13-4/7+6/13

=1-4/7

=3/7

a,17/23 + (1 - 17/23)

= 17/23 + 6/23

= 23/23 = 1

b,17/12 + 9/7 - (2/7 + 5 /12)

= (17/12 - 5/12) + (9/7 + 2/7)

= 1+1 = 2

c, 7/13 - ( 4/7 -6/13 )

= 7/13 - 4/7+ 6/13

= (7/13 + 6/13) -4/7

= 13/13 -4/7

= 1 -4/7 = 3/7

hok tốt✍️ ✍️

Lấy các số cùng mẫu gộp lại tính trước 

a) 17/23 + (1 - 17/23)

= 17/23 + 1 - 17/23

= (17/23 - 17/23)  + 1

= 0 + 1 = 1

b) 17/12 + 9/7 - (2/7 + 5/12)

= 17/12 + 9/7 - 2/7 - 5/12

= (17/12  - 5/12) + (9/7 - 2/7)

= 1 + 1 = 2

c) 7/13 - (4/7 - 6/13)

= 7/13 - 4/7 + 6/13

= (6/13 + 6/12) - 4/7

= 1 - 4/7 = 3/7

d) 7/18 + 3/16 + 11/18 + 13/16

= (7/18 + 11/18) + (3/16 + 13/16)

= 1 + 1 = 1

d) sửa 7/18 + 3/16 + 11/18 + 13/16

= (7/18 + 11/18) + (3/16 + 13/16)

= 1 + 1

= 2