12/18 + 12/42 = 2/3 + 2/7 = 14/21 + 6/21 = 20/21

1/2 + 2/4 + 3/6 + 4/8 + 5/10 + 6/12

= 1/2 + 1/2 + 1/2 + 1/2 + 1/2 + 1/2

= 1/2 x 6

=6/2

=3

Còn phần D thì sao😶

tra hieu gi ca

1.

a, Ta có 28=14⇒14+56=1312(Bn tự quy đồng lên nhé !)

b,Ta có1216=34⇒18+34=78(Bn tự quy đồng lên nhé !)

c,Ta có636=16⇒14+16=512(Bn tự quy đồng lên nhé !)

d,Ta có1218=23⇒23+14=1112(Bn tự quy đồng lên nhé !)

7.Phần này mk chỉ cho đáp án thuia.67     ;     

 b,420=15     ;         

c,615       ;            

d,129

a) \(\dfrac{4}{5}+\dfrac{3}{15}=\dfrac{4}{5}+\dfrac{1}{5}=\dfrac{5}{5}=1\)

b) \(\dfrac{2}{3}+\dfrac{32}{24}=\dfrac{2}{3}+\dfrac{4}{3}=\dfrac{6}{3}=2\)

c) \(\dfrac{5}{6}+\dfrac{15}{18}=\dfrac{5}{6}+\dfrac{5}{6}=\dfrac{10}{6}=\dfrac{5}{3}\).

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, 

1, Rút gọn rồi tính 

a) \(\frac{4}{5}+\frac{3}{15}\)

= \(\frac{4}{5}+\frac{1}{5}\)

= \(\frac{5}{5}\)

= \(1\)

b) \(\frac{2}{3}+\frac{32}{24}\)

= \(\frac{2}{3}+\frac{4}{3}\)

= \(\frac{6}{3}\)

= \(2\)

c) \(\frac{5}{6}+\frac{15}{18}\)

= \(\frac{5}{6}+\frac{5}{6}\)

= \(\frac{10}{6}\)

= \(\frac{5}{3}\)

2, Tính rồi rút gọn 

a) \(\frac{8}{15}+\frac{2}{3}\)

= \(\frac{8}{15}+\frac{10}{15}\)

= \(\frac{18}{15}\)

= \(\frac{6}{5}\)

b) \(\frac{3}{7}+\frac{4}{8}\)

= \(\frac{24}{56}+\frac{28}{56}\)

= \(\frac{52}{56}\)

= \(\frac{13}{14}\)

Đáp án:

a) 1

b) 2

c) 5/3

Bài 3.Tính rồi rút gọn

a)6/5

b) 13/14

a) 4/5+3/15=4/5+1/5=1

b) 2/3+32/24=2/3+4/3=2

c)5/6+15/18=5/6+5/6=5/3

3.

a)8/15+2/3=18/15=6/5

b)3/7+4/8=52/56=13/14

Nhớ k cho mình đó !

Đã hứa thì phải làm