Nay rảnh lại qua làm mấy bài lớp 4 ^^

Tui làm luôn kh ghi đề nhá

1, 

\(\frac{2}{3}+\frac{8}{15}=\frac{6}{5}\)

\(\frac{2}{5}+\frac{2}{3}=\frac{16}{15}\)

\(\frac{2}{3}+\frac{5}{6}=\frac{3}{2}\)

2, 

\(\cdot\frac{3}{7}+\frac{6}{5}+\frac{4}{7}\)

\(=\frac{3}{7}+\frac{4}{7}+\frac{6}{5}\)

\(=1+\frac{6}{5}\)

\(=\frac{11}{5}\)

\(\cdot\frac{6}{4}+\frac{7}{3}+\frac{4}{4}+\frac{3}{3}\)

\(=\frac{6}{4}+\frac{4}{4}+\frac{7}{3}+\frac{3}{3}\)

\(=\frac{10}{4}+\frac{10}{3}\)

\(=\frac{35}{6}\)

2, 

2/3 + 3/4=17/12
9/4 + 3/5=57/20
5/24 + 1/4=11/24
3/15 - 5/35=2/35        18/27 - 2/6=1/3        37/12 - 3=1/12
11/9 x 3/22=1/6         7/13 x 13/7=1       4 x6/7=24/7
2/5 : 3/10=4/3           3/8 : 9/4=1/6            8/21 : 4/7=2/3

2/3 + 3/4

= 17/12
9/4 + 3/5

= 57/20
5/24 + 1/4

=11/24
3/15 - 5/35   

=2/35   

18/27 - 2/6   

=1/3   

37/12 - 3

= 1/12
11/9 x 3/22 

=1/6       

7/13 x 13/7 

=1   

 4 x6/7

=24/7
2/5 : 3/10

=4/3         

 3/8 : 9/4   

=1/6       

8/21 : 4/7

= 2/3

a: =6/12*7/14*8/16*9/18=1/2*1/2*1/2*1/2=1/16

b: =4/12*15/3*9/25*24/8

=1/3*3*5*9/25=9/5

a: \(-\frac{10}{3}+\frac{13}{10}-\frac16+\frac{7}{10}\)

\(=\left(-\frac{10}{3}-\frac16\right)+\left(\frac{13}{10}+\frac{7}{10}\right)\)

\(=-\frac{21}{6}+\frac{20}{10}=-\frac72+2=-\frac32\)

b: \(1-\frac{20}{6}+\frac{39}{30}-\frac{4}{24}+\frac{34}{50}\)

\(=1-\frac{20}{6}+\frac16+1,3+0,68\)

\(=1-\frac{19}{6}+1,98=2,98-\frac{19}{6}=\frac{298}{100}-\frac{19}{6}=\frac{-56}{300}=\frac{-14}{75}\)

c: \(\frac{15}{24}-\frac{6}{26}+\frac{28}{48}-\frac{30}{39}+\frac{10}{24}\)

\(=\left(\frac{15}{24}+\frac{10}{24}+\frac{28}{48}\right)-\left(\frac{3}{13}+\frac{10}{13}\right)\)

\(=\left(\frac{25}{24}+\frac{14}{24}\right)-1=\frac{39}{24}-1=\frac{15}{24}=\frac58\)

d: \(-\frac{5}{10}+\frac{12}{28}-\frac{3}{27}-\frac{7}{18}+\frac{20}{35}\)

\(=-\frac12+\frac37-\frac19-\frac{7}{18}+\frac47\)

\(=\left(-\frac12-\frac19-\frac{7}{18}\right)+\left(\frac37+\frac47\right)=-1+1=0\)

cau 1 sai de

cau 2 :

3+6+9+12+15+18+21+24+27= (3+27)+(6+34)+(9+21)+(12+18)+15= 30+30+30+30+15=135

\(1+2+3+4+5+...+28+29=\left(1+29\right).29:2=435\)

(1+29)+(2+28)+(3+27)+(4+26)+(5+25)+(6+24)+(7+23)+(8+22)+(9+21)+(10+20)+(11+19)+(12+18)+(13+17)+(14+16)+15

=30+30+30+30+30+30+30+30+30+30+30+30+30+30+15

=30x14+15

=435

=-3720

đồ bấm máy tính ko chấp

B=2006 * 2008 -3 / 2005 + 2005 * 2008

B=(2005+1)* 2008 -3 / 2005 +2005 *2008

B=2005 * 2008 + 2008 -3 / 2005 +2005*2008

B=2005 * 2008 + 2005 / 2005 +2005 * 2008

B= 1

khi nào 2-1=3?