2 / 3 + 3 / 4 = 8 / 12 + 9 / 12 = 17 / 12
5 / 6 - 1 /3 = 15 / 18 - 6 / 18 = 9 / 18
2 / 5 x 15 / 8 = 30 / 40
1 / 2 : 2 / 5 = 1 / 2 x 5 / 2 = 5 / 4
bài 1:
a, 2/3 + 3/4 = 8/12 + 9/12= 17/12
b, 5/6 - 1/3 = 5/6 - 2/6 = 3/6 = 1/2
c, 2/5 x 15/8= 3/4
d,1/2 : 2/5 = 5/4
\(1.\)
\(a,\dfrac{2}{3}+\dfrac{3}{4}=\dfrac{8}{12}+\dfrac{9}{12}=\dfrac{8+9}{12}=\dfrac{17}{12}\)
\(b,\dfrac{5}{6}-\dfrac{1}{3}=\dfrac{5}{6}-\dfrac{2}{6}=\dfrac{3}{6}=\dfrac{1}{2}\)
\(c,\dfrac{2}{5}\times\dfrac{15}{8}=\dfrac{2\times15}{5\times8}=\dfrac{30}{40}=\dfrac{3}{4}\)
\(d,\dfrac{1}{2}:\dfrac{2}{5}=\dfrac{1\times5}{2\times2}=\dfrac{5}{4}\)
\(2.\)
\(a,\dfrac{1}{3}+\dfrac{4}{3}\times\dfrac{1}{2}=\dfrac{1}{3}+\left(\dfrac{4}{3}\times\dfrac{1}{2}\right)=\dfrac{1}{3}+\dfrac{2}{3}=\dfrac{1+2}{3}=\dfrac{3}{3}=1\)
\(b,\dfrac{3}{5}\times\dfrac{4}{7}:\dfrac{16}{21}=\dfrac{12}{35}:\dfrac{16}{21}=\dfrac{12\times21}{35\times16}=\dfrac{252}{560}=\dfrac{9}{20}\)
bài 2:
1/3 + 4/3 x 1/2 3/5 x 4/7: 16/21
= 1/3 + 2/3 = 12/35 : 16/21
= 1 = 63/ 140
Bài 1
a) \(\dfrac{2}{3}+\dfrac{3}{4}=\dfrac{8}{12}+\dfrac{9}{12}=\dfrac{17}{12}\)
b) \(\dfrac{5}{6}-\dfrac{1}{3}=\dfrac{5}{6}-\dfrac{2}{6}=\dfrac{4}{6}=\dfrac{2}{3}\)
c) \(\dfrac{2}{5}\times\dfrac{15}{8}=\dfrac{30}{40}=\dfrac{15}{20}=\dfrac{3}{4}\)
d) \(\dfrac{1}{2}\div\dfrac{2}{5}=\dfrac{1}{2}\times\dfrac{5}{2}=\dfrac{5}{4}\)
Bài 2
a) \(\dfrac{1}{3}+\dfrac{4}{3}\times\dfrac{1}{2}=\dfrac{1}{3}+\dfrac{4}{6}=\dfrac{1}{3}+\dfrac{2}{3}=\dfrac{3}{3}=1\)
b) \(\dfrac{3}{5}\times\dfrac{4}{7}\div\dfrac{16}{21}=\dfrac{12}{35}\div\dfrac{16}{21}=\dfrac{12}{35}\times\dfrac{21}{16}=\dfrac{9}{20}\)
Bài 3
Chiều rộng thửa ruộng là :
\(120\times\dfrac{3}{5}=72\left(m\right)\)
Chu vi thửa ruộng là :
\(\left(120+72\right)\times2=384\left(m\right)\)
Diện tích thửa ruộng là :
\(120\times72=8640\left(m^2\right)\)
Đ/s : Chu vi :\(384m\)
Diện tích : \(8640m^2\)
Bài 4
Số lớn là :
\(\left(\dfrac{4}{7}+\dfrac{1}{2}\right)\div2=\dfrac{15}{28}\)
Số bé là :
\(\dfrac{4}{7}-\dfrac{15}{28}=\dfrac{1}{28}\)
