Phép cộng phân số (tiếp theo)

\(\dfrac{2}{5}+\dfrac{4}{7}=\dfrac{14}{35}+\dfrac{20}{35}=\dfrac{34}{35}\)

\(\dfrac{3}{5}+\dfrac{4}{3}=\dfrac{9}{15}+\dfrac{20}{15}=\dfrac{29}{15}\)

\(\dfrac{14}{35}+\dfrac{20}{35}=\dfrac{34}{35}\)

\(\dfrac{9}{15}+\dfrac{20}{15}=\dfrac{29}{15}\)

Bài 2: 

a: 3/12+1/4=1/4+1/4=2/4=1/2

b: 4/25+3/5=4/25+15/25=19/25

c: 26/81+4/27=26/81+12/81=38/81

d: 5/64+7/8=5/64+56/64=61/64

\(\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{12}=\dfrac{4}{12}+\dfrac{2}{12}+\dfrac{1}{12}=\dfrac{7}{12}\)

\(=\dfrac{4}{12}+\dfrac{2}{12}+\dfrac{1}{12}=\dfrac{7}{12}\)

\(\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{12}=\dfrac{4}{12}+\dfrac{2}{12}+\dfrac{1}{12}=\dfrac{7}{12}\)

\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26+12}{81}=\dfrac{38}{81}\)

\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5+56}{64}=\dfrac{61}{64}\)

\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26}{81}+\dfrac{4\times3}{27\times3}=\dfrac{26}{81}+\dfrac{12}{81}=\dfrac{38}{81}\)

\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5}{64}+\dfrac{7\times8}{8\times8}=\dfrac{5}{64}+\dfrac{56}{64}=\dfrac{61}{64}\)

3/7 + 4/5 = 15/35 + 28/35 = 43/35

7/15 + 2/5 = 7/15 + 6/15 = 13/15

a 43/35

b 13/15

a, 43/35

b, 13/15

Nửa chu vi hình chữ nhật trên là:
\(\dfrac{1}{4}+\dfrac{12}{5}=\dfrac{53}{20}\left(m\right)\)

Đáp số: \(\dfrac{53}{20}m\)

\(\dfrac{1}{4}< x< \dfrac{2}{5}\)

=>\(\dfrac{5}{20}< x< \dfrac{8}{20}\)

\(\Rightarrow x\in\left\{\dfrac{6}{20};\dfrac{7}{20}\right\}\)

Vậy \(x\in\left\{\dfrac{6}{20};\dfrac{7}{20}\right\}\)

Chúc bn học tốt

\(\dfrac{1}{4}< a,b< \dfrac{2}{5}\)

\(\Leftrightarrow\dfrac{5}{20}< a,b< \dfrac{8}{20}\)

\(\Rightarrow a=\dfrac{6}{20}=\dfrac{3}{10}\\ ,b=\dfrac{7}{20}\)

\(\dfrac{1}{4}< \dfrac{3}{10}< \dfrac{7}{20}< \dfrac{2}{5}\)

\(\dfrac{105}{135}\)

105/135

105/135=7/9

Sau hai ngày, công nhân đó hái được 17/100+7/50=17/100+14/100=31/100=0,31 tấn cà phê

2 ngày hái dc : \(\dfrac{17}{100}+\dfrac{7}{50}=\dfrac{17}{100}+\dfrac{14}{100}=\dfrac{31}{100}\left(t\text{ấn}\right)\)

31/100 tấn  hoặc 0,31 tấn

a: 5/6+1/2=5/6+3/6=8/6=4/3

b: 7/8+1/4=7/8+2/8=9/8

c: 5/9+3/7=35/63+27/63=62/63

\(a,\dfrac{5}{6}+\dfrac{1}{2}=\dfrac{4}{3}\\ b,\dfrac{7}{8}+\dfrac{1}{4}=\dfrac{9}{8}\\ c,\dfrac{5}{9}+\dfrac{3}{7}=\dfrac{62}{63}\)

\(a,\dfrac{5}{6}+\dfrac{1\times3}{2\times3}=\dfrac{5}{6}+\dfrac{3}{6}=\dfrac{8}{6}=\dfrac{4}{3}\\ b,\dfrac{7}{8}+\dfrac{1\times2}{4\times2}=\dfrac{7}{8}+\dfrac{2}{8}=\dfrac{9}{8}\\ c,\dfrac{5\times7}{9\times7}+\dfrac{3\times9}{7\times9}=\dfrac{35}{63}+\dfrac{27}{63}=\dfrac{62}{63}\)