Tính 4 7 x 7 4
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a) Cách 1 : (3/4 + 1/2) x 5/7
= 5/4 x 5/7
= 25/28
Cách 2 : (3/4 + 1/2) x 5/7
= 3/4 x 5/7 + 1/2 x 5/7
= 15/28 + 5/14
= 25/28
b) Cách 1 : 5/7 x 13/21 + 2/7 x 13/21
= 65/147 + 26/147
= 13/21
Cách 2 : 5/7 x 13/21 + 2/7 x 13/21
= (5/7 + 2/7) x 13/21
= 1 x 13/21
= 13/21
câu c tự làm
7 x 2 = 14
4 x 7 = 28
7 x 6 = 42
3 x 7 = 21
5 x 7 = 35
2 x 7 = 14
7 x 4 = 28
6 x 7 = 42
7 x 3 = 21
7 x 5 = 35
7 x 2 = 14
4 x 7 = 28
7 x 6 = 42
3 x 7 = 21
5 x 7 = 35
2 x 7 = 14
7 x 4 = 28
6 x 7 = 42
7 x 3 = 21
7 x 5 = 35
\(\frac{4}{7}.\frac{5}{12}+\frac{4}{7}.\frac{7}{12}+\frac{4}{7}\)
\(=\frac{4}{7}.\left(\frac{5}{12}+\frac{7}{12}+1\right)\)
\(=\frac{4}{7}\left(\frac{12}{12}+1\right)\)
\(=\frac{4}{7}.2\)
\(=\frac{8}{7}\)
Học sinh nhẩm và ghi kết quả như sau:
7 x 5 = 35
7 x 6 = 42
7 x 2 = 14
7 x 4 = 28
35 : 7 =5
42 : 7 = 6
14 : 7 = 2
28: 7 =4
35 : 5 = 7
42 : 6 = 7
14 : 2 = 7
28 : 4 = 7
7 x 4 - 7 x 6/14 x 6 - 7 x 4
=7 x 4 - 7 x 18/7 - 7 x 4
=7x(4 - 18/7 - 4 )
=7 x (-18/7)
=-18
a)2/3*4/7+1/3*4/7=(2/3+1/3)*4/7=1*4/7=4/7
b)5/8*3/7*7/3=5/8*1=5/8
c)(4/5+2)*5/4=4/5*5/4+2=1+2=3
\(a,5x\dfrac{7}{3}=\dfrac{5}{1}x\dfrac{7}{3}=\dfrac{35}{3};b,\dfrac{13}{4}:7=\dfrac{13}{4} :\dfrac{7}{1}=\dfrac{13}{4}x\dfrac{1}{7}=\dfrac{13}{28}\)
1. Tính
\(a,5\times\dfrac{7}{3}=\dfrac{35}{3}\)
\(b,\dfrac{13}{4}:7=\dfrac{13}{4}\times\dfrac{1}{7}=\dfrac{13}{28}\)
2. Tính
\(a,\dfrac{3}{7}+\dfrac{2}{5}+\dfrac{3}{4}\)
\(=\dfrac{15}{35}+\dfrac{14}{35}+\dfrac{3}{4}\)
\(=\dfrac{29}{35}+\dfrac{3}{4}\)
\(=\dfrac{116}{140}+\dfrac{105}{140}\)
\(=\dfrac{221}{140}\)
\(b,\dfrac{9}{7}-\dfrac{5}{11}\times\dfrac{11}{7}\)
\(=\dfrac{9}{7}-\dfrac{55}{77}\)
\(=\dfrac{99}{77}-\dfrac{55}{77}\)
\(=\dfrac{44}{77}=\dfrac{4}{7}\)
\(c,\dfrac{3}{5}\times\dfrac{5}{7}+\dfrac{4}{7}\)
\(=\dfrac{3}{5}\times\left(\dfrac{5}{7}+\dfrac{4}{7}\right)\)
\(=\dfrac{3}{5}\times\dfrac{9}{7}\)
\(=\dfrac{27}{35}\)
\(d,\dfrac{7}{9}\times\dfrac{2}{5}:\dfrac{3}{11}\)
\(=\dfrac{14}{45}:\dfrac{3}{11}\)
\(=\dfrac{14}{45}\times\dfrac{11}{3}\)
\(=\dfrac{154}{135}\)
\(e,\dfrac{9}{7}+\dfrac{2}{3}-\dfrac{1}{4}\)
\(=\dfrac{27}{21}+\dfrac{14}{21}-\dfrac{1}{4}\)
\(=\dfrac{41}{21}-\dfrac{1}{4}\)
\(=\dfrac{164}{84}-\dfrac{21}{84}\)
\(=\dfrac{143}{84}\)
\(g,\dfrac{4}{9}:\dfrac{3}{5}\times\dfrac{2}{11}\)
\(=\dfrac{4}{9}\times\dfrac{5}{3}\times\dfrac{2}{11}\)
\(=\dfrac{20}{27}\times\dfrac{2}{11}\)
\(=\dfrac{40}{297}\)
\(h,\dfrac{7}{2}-\dfrac{3}{10}:\dfrac{2}{5}\)
\(=\left(\dfrac{7}{2}-\dfrac{3}{10}\right):\dfrac{2}{5}\)
\(=\left(\dfrac{35}{10}-\dfrac{3}{10}\right):\dfrac{2}{5}\)
\(=\dfrac{32}{10}:\dfrac{2}{5}\)
\(=\dfrac{16}{5}\times\dfrac{5}{2}\)
\(=\dfrac{80}{10}=8\)
4 7 x 7 4 = 1