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câu a bằng 15/8
câu b bằng 19/6
câu c bằng 3/10
câu d bằng 27/4
`a, 4/9 + 2/5 + 5/9= (4/9 +5/9) + 2/5= 1 + 2/5= 5/5 + 2/5= 7/5`
`b, 6/13 + 5/8 + 7/13=(6/13 + 7/13) + 5/8=1+5/8= 8/8 + 5/8= 13/8`
`c, 5/11 + 6/25 + 66/121 = ( 5/11 + 66/121 ) + 6/25=1 + 6/25 = 25/25 + 6/25 = 31/25`
`d, 1/2 + 1/3 + 1/4 + 1/6 + 1/12 + 1/24= (1/2 + 1/4) +(1/3 + 1/6) + (1/12 + 1/24)= 3/4 + 1/2 + 1/8= 6/8 + 4/8 + 1/8= 11/8`
`@ yl`
a)\(=\dfrac{16}{13}-\dfrac{3}{15}+\dfrac{6}{13}=\dfrac{22}{13}-\dfrac{3}{15}=\dfrac{96}{65}\)
b)\(=\dfrac{21}{8}-\left(\dfrac{5}{10}+\dfrac{6}{10}\right)=\dfrac{21}{8}-\dfrac{11}{10}=\dfrac{61}{40}\)
c)\(=\dfrac{27}{10}-3-\dfrac{4}{7}--\dfrac{61}{70}\)
a] 4/12 ; 5/12 ; 11/2 ; 1/4
b] 1 ; 9/12; 12/5 ; 11/3
c] 8/21; 6/11;8/7
d] 2/3 ;2/7 15/2
a]1/3 5/12 11/2 1/4
b]1 3/4 12/5 33/9
c]8/21 6/11 8/7
d]2/3 2/7 15/2
bài 1 :
\(a,\dfrac{2}{7}+\dfrac{1}{3}=\dfrac{6}{21}+\dfrac{7}{21}=\dfrac{13}{21}\)
\(b,\dfrac{3}{5}-\dfrac{1}{3}=\dfrac{9}{15}-\dfrac{5}{15}=\dfrac{4}{15}\)
\(c,\dfrac{13}{4}:5=\dfrac{13}{4}:\dfrac{5}{1}=\dfrac{13}{4}x\dfrac{1}{5}=\dfrac{13}{20}\)
\(d,\dfrac{6}{23}x\dfrac{1}{18}=\dfrac{1}{69}\)
bài 2 :
\(a,x+\dfrac{1}{3}=\dfrac{5}{12}\)
\(x=\dfrac{5}{12}-\dfrac{1}{3}\)
\(x=\dfrac{1}{12}\)
\(b,x:\dfrac{7}{4}=\dfrac{2}{5}\)
\(x=\dfrac{2}{5}x\dfrac{7}{4}\)
\(x=\dfrac{7}{10}\)
bài 3 :
đổi : 2 dm 1cm = 21cm
chiều cao hình bình hành là;
21 x\(\dfrac{3}{7}=\)9(cm)
diện tích hình bình hành là;
21 x 9 =189 (cm2)
đáp số : 189 cm2
bài 4 :
\(\dfrac{2}{3}x\dfrac{2}{10}+\dfrac{2}{3}x\dfrac{5}{10}x\dfrac{3}{3}\)
\(\dfrac{2}{3}x\left(\dfrac{2}{10}+\dfrac{5}{10}\right)x\dfrac{2}{3}\)
=\(\dfrac{2}{3}x1x\dfrac{2}{3}\)
\(=\dfrac{2}{3}x\dfrac{2}{3}\)
=\(\dfrac{4}{9}\)
Bài 1)
a) \(\dfrac{6}{21}+\dfrac{7}{21}=\dfrac{13}{21}\)
b) \(\dfrac{9}{15}-\dfrac{5}{15}=\dfrac{4}{15}\)
c) \(\dfrac{13}{4}x\dfrac{1}{5}=\dfrac{13}{20}\)
d) \(\dfrac{6}{414}=\dfrac{1}{69}\)
Bài 2)
a) \(x=\dfrac{5}{12}-\dfrac{1}{3}\)
\(x=\dfrac{1}{12}\)
b) \(x=\dfrac{2}{5}x\dfrac{7}{4}\)
\(x=\dfrac{7}{10}\)
Bài 3)
2dm 1cm = 21 cm
Chiều cao tấm bìa la
\(21x\dfrac{3}{7}=9\left(cm\right)\)
Diện tích tấm bìa là
\(21x9=189\left(cm2\right)\)
\(a,\dfrac{5}{9}+\dfrac{3}{8}=\dfrac{40}{72}+\dfrac{27}{72}=\dfrac{67}{72}\)
\(b,\dfrac{8}{12}-\dfrac{1}{3}=\dfrac{8}{12}-\dfrac{4}{12}=\dfrac{4}{12}=\dfrac{1}{3}\)
\(c,\dfrac{4}{7}\times\dfrac{5}{2}=\dfrac{20}{14}=\dfrac{10}{7}\)
\(d,\dfrac{5}{11}:\dfrac{15}{22}=\dfrac{5}{11}\times\dfrac{22}{15}=\dfrac{110}{165}=\dfrac{22}{33}\)
a: =2/5x11/7=22/35
b: =60/85+68/85=128/75
c: =78/143-44/143=34/143
d: =5/6+8/21=35/42+16/42=51/42=17/14
a)5/12 + 1/4 = \(\dfrac{5}{12}+\dfrac{3}{12}=\dfrac{8}{12}=\dfrac{2}{3}\)
b)23/5 - 11/3 = \(\dfrac{69}{15}-\dfrac{55}{15}=\dfrac{14}{15}\)
c)4/5 + 13 = \(\dfrac{4}{5}+\dfrac{65}{5}=\dfrac{69}{5}\)
d)8/5 : 1/3 = \(\dfrac{8}{5}x3=\dfrac{24}{5}\)
e)3/7 x 2 =\(\dfrac{6}{7}\)
\(a,\) \(\dfrac{5}{12}+\dfrac{1}{4}=\dfrac{5}{12}+\dfrac{3}{12}=\dfrac{8}{12}=\dfrac{2}{3}\)
\(b,\) \(\dfrac{23}{5}-\dfrac{11}{3}=\dfrac{69}{15}-\dfrac{55}{15}=\dfrac{14}{15}\)
\(c,\) \(\dfrac{4}{5}+\dfrac{1}{3}=\dfrac{12}{15}+\dfrac{5}{15}=\dfrac{17}{15}\)
\(d,\) \(\dfrac{8}{5}:\dfrac{1}{3}=\dfrac{8}{5}\times\dfrac{3}{1}=\dfrac{24}{5}\)
\(e,\) \(\dfrac{3}{7}\times2=\dfrac{3\times2}{7}=\dfrac{6}{7}\)