9976+865)+135=976+(865+135)=976+1000=1976

891+(799+109)=(891+109)+799=1000+799=1799

(2/5+1/9)+3/5=(2/5+3/5)+1/9=1+1/9=9/9+1/9=10/9

19/11+(8/13+3/11)=(19/11+3/11)+8/13=22/11+8/13=22/11+8/13=2+8/13=26/13+8/13=34/13

16.88+9.76+3.12=(16.88+3.12)+9.76=20+9.76=29.76

72.68+17.16+82.64=72.68+(17.16+82.64)=72.68+100=172.68

(976+865)+135=976+(865+135)

                      =976+1000=1976

Blox fruits V 100000000000000000

1. (976 + 865) + 135 = 976 + 865 + 135 = 976 + (865 + 135) = 975 + 1000 = 1975

891 + (799 + 109) = 891 + 799 + 109 = (891 + 109) + 799 = 1000 + 799 = 1799

(2/5 + 7/9) + 3/5 = 2/5 + 7/9 + 3/5 = (2/5 + 3/5) + 7/9 = 1 + 7/9 = 16/9

2) 1 phút = 60 giây = 1/60 giờ

   1 giây = 1/60 phút = 1/3600 giờ

2. Viết số thích hợp:

1 phút =....60.....giây =......1/60...giờ

1 giây =...1/60......phút =..1/3600.......giờ

Bài 1:

\(\left(976+865\right)+135=976+\left(865+135\right)=976+1000=1976\)

\(891+\left(799+109\right)=\left(891+109\right)+799=1000+799=1799\)

\(\left(\frac{2}{5}+\frac{7}{9}\right)+\frac{3}{5}=\left(\frac{2}{5}+\frac{3}{5}\right)+\frac{7}{9}=1+\frac{7}{9}=\frac{16}{9}\)

\(\frac{19}{11}+\left(\frac{8}{13}+\frac{3}{11}\right)=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{8}{13}=2+\frac{8}{13}=\frac{34}{13}\)

Bài 2:

1 phút = 60 giây = \(\frac{1}{60}\)giờ

1 giây = \(\frac{1}{60}\)phút = \(\frac{1}{3600}\)giờ

~Học tốt~

1976

16/9

34/13

1976

16/9

34/13

1976

16/9

34/13

1

 9/11         6/5       19/14       21/18

2 tự làm

3 lớp 4 có số thập phân ak 

 1b   4/11+5/11=9/11     ;2/3+4/5=10/15+12/15=22/15      ;5/7+9/14=10/14+9/14=19/14       ;2+5/8=2/2+5/8=8/8+5/8=13/8

a)   (865+135)+976=1000+976=1976        

(891+109)+799=1000+799=1799   

(2/5+3/5)+7/9=1+7/9=16/9

(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+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

=  20x9 +30

=180+30

=210

tk cho mik nhé

\(\frac{\left(20+1\right)x20}{2}\)

=(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+10

=190

210 bạn nha

tk mình nhé

(20+1)x20:2=210

bằng 210 đúng ko