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\(a,\dfrac{7}{9}\times\dfrac{3}{14}:\dfrac{5}{8}=\dfrac{7}{9}\times\dfrac{3}{14}\times\dfrac{8}{5}=\dfrac{4}{15}\)
\(b,\dfrac{3}{5}\times\dfrac{4}{21}\times\dfrac{25}{3}=\dfrac{20}{21}\)
\(c,\dfrac{15}{16}:\dfrac{5}{8}\times\dfrac{3}{4}=\dfrac{15}{16}\times\dfrac{8}{5}\times\dfrac{3}{4}=\dfrac{9}{8}\)
\(d,\dfrac{21}{4}\times\dfrac{16}{14}\times\dfrac{1}{2}\times\dfrac{8}{3}=8\)
12/21:3/7=4/3
4/9x3/8=1/6
4/3x9/20=3/5
5/12:25/24=2/5
bài được viết thành phân số tối giản
Bài 1:
\(\frac{15}{4}=3\frac{3}{4}\)
\(\frac{25}{4}=6\frac{1}{4}\)
\(\frac{1456}{78}=18\frac{2}{3}\)
\(\frac{11198}{796}=14\frac{27}{398}\)
Bài 2 :
\(\frac{1}{9}+\frac{2}{8}=\frac{13}{36}\)
\(\frac{1}{2}-\frac{1}{9}=\frac{7}{18}\)
\(\frac{5}{6}x\frac{2}{8}=\frac{5}{24}\)
\(\frac{3}{8}:\frac{2}{6}=\frac{9}{8}\)
bài 3:
Số học sinh của lớp đó là :
\(21:\frac{7}{10}=30\) ( em )
Đ/s: 30 em
A = 3/1×5 + 3/5×9 + 1/9×13 + ... + 9/97×101 + 3/101×105
A = 3/4 × (4/1×5 + 4/5×9 + 4/9×13 + ... + 4/97×101 + 4/101×105)
A = 3/4 × (1 - 1/5 + 1/5 - 1/9 + 1/9 - 1/13 + ... + 1/97 - 1/101 + 1/101 - 1/105)
A = 3/4 × (1 - 1/105)
A = 3/4 × 104/105
A = 26/35
B = 1/5 + 1/25 + 1/125 + 1/625 + 1/3125 + 1/15625
5B = 1 + 1/5 + 1/25 + 1/125 + 1/625 + 1/3125
5B - B = (1 + 1/5 + 1/25 + 1/125 + 1/625 + 1/3125) - (1/5 + 1/25 + 1/125 + 1/625 + 1/3125 + 1/15625)
4B = 1 - 1/15625
4B = 15624/15625
B = 15624/15625 : 4
B = 3906/15625
C = 1 + 2 + 4 + 8 + 16 + ... + 2048 + 4096
2C = 2 + 4 + 8 + 16 + 32 + ... + 4096 + 8192
2C - C = (2 + 4 + 8 + 16 + 32 + ... + 4096 + 8192) - (1 + 2 + 4 + 8 + ... + 2048 + 4096)
B = 8192 - 1
B = 8191
\(3\dfrac{1}{3}+\dfrac{5}{6}=\dfrac{10}{3}+\dfrac{5}{6}=\dfrac{20}{6}+\dfrac{5}{6}=\dfrac{25}{6}\)
\(4\dfrac{5}{7}-2\dfrac{11}{21}=\dfrac{33}{7}-\dfrac{53}{21}=\dfrac{99}{21}-\dfrac{53}{21}=\dfrac{46}{21}\)
\(3\dfrac{1}{4}x\dfrac{2}{5}=\dfrac{13}{3}x\dfrac{2}{5}=\dfrac{26}{15}\)
\(4\dfrac{7}{8}:\dfrac{1}{4}=\dfrac{39}{8}.4=\dfrac{39}{2}\)
(6-14/5)×25/8-18/5×1/4
=16/5 * 25/8 - 18/5 * 1/4
=10 - 9/10
=91/10
4 và 2/5-1 và 3/7-1 và 4/7
=22/5 - 10/7 - 11/7
=104/35 - 11/7
=7/5
8/11×(7/4-3/8)
=8/11 * 11/8
=1
8/5×(3/7+1/4)
=8/5 * 3/28
=6/35
a: \(x+\dfrac{3}{9}=\dfrac{7}{6}\cdot\dfrac{2}{3}\)
=>\(x+\dfrac{1}{3}=\dfrac{14}{18}=\dfrac{7}{9}\)
=>\(x=\dfrac{7}{9}-\dfrac{1}{3}=\dfrac{7}{9}-\dfrac{3}{9}=\dfrac{4}{9}\)
b: \(x-\dfrac{2}{3}=\dfrac{1}{8}:\dfrac{5}{4}\)
=>\(x-\dfrac{2}{3}=\dfrac{1}{8}\cdot\dfrac{4}{5}=\dfrac{1}{10}\)
=>\(x=\dfrac{1}{10}+\dfrac{2}{3}=\dfrac{3+20}{30}=\dfrac{23}{30}\)
\(\dfrac{8}{13}+\dfrac{4}{9}+\dfrac{1}{3}+\dfrac{5}{13}+3\)
\(=1+\dfrac{7}{9}+3\)
\(=4+\dfrac{7}{9}=\dfrac{43}{9}\)
4/5x 5/6x6/7:8/21
= 2/3 x 6/7 : 8/21
= 4/7 : 8/21
= 3/2
5/6x2/3+1/6x2/3
= 5/9 + 1/9
= 2/3
4/7x1/2-1/7x1/2
= 2/7 - 1/14
= 3/14
8/9x3/4-5/9x3/4
= 2/3 - 5/12
= 1/4
\(\dfrac{3}{2}\)
\(\dfrac{2}{3}\)
\(\dfrac{3}{14}\)
\(\dfrac{1}{4}\)