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Câu 1:\(\frac{12}{23}\times\frac{9}{28}+\frac{11}{23}\times\frac{9}{28}\)
\(=\frac{9}{28}\times\left(\frac{12}{23}+\frac{11}{23}\right)\)
\(=\frac{9}{28}\times\frac{23}{23}\)
\(=\frac{9}{28}\times1\)
\(=\frac{9}{28}\)
Câu 2:
\(3+\frac{1}{9}+\frac{3}{9}+2+\frac{5}{9}+3+2\)
\(=\left(3+2+2+3\right)+\left(\frac{1}{9}+\frac{3}{9}+\frac{5}{9}\right)\)
\(=10+\frac{9}{9}\)
\(=10+1\)
\(=11\)
\(\frac{12}{23}x\frac{9}{28}+\frac{11}{23}x\frac{9}{28}=\)\(\left(\frac{12}{23}+\frac{11}{23}\right)x\frac{9}{28}\)\(=\) \(1x\frac{9}{28}=\frac{9}{28}\)
\(3+\frac{1}{9}+\frac{3}{9}+2+\frac{5}{9}+3+2\)\(=\) \(\left(\frac{1}{9}+\frac{3}{9}+\frac{5}{9}\right)+\left(3+2+3+2\right)\)\(=\) \(1+3+2+3+2=\)\(11\)
a) \(\frac{3}{5}+\frac{4}{7}+\frac{2}{5}+\frac{1}{7}+\frac{2}{7}\)
\(=\left(\frac{3}{5}+\frac{2}{5}\right)+\left(\frac{4}{7}+\frac{1}{7}+\frac{2}{7}\right)\)
\(=\frac{5}{5}+\frac{7}{7}=1+1=2\)
a) \(\frac{3}{5}+\frac{4}{7}+\frac{2}{5}+\frac{1}{7}+\frac{2}{7}\)
\(=\left(\frac{3}{5}+\frac{2}{5}\right)+\left(\frac{4}{7}+\frac{1}{7}+\frac{2}{7}\right)\)
= 1 + 1
= 2
b) \(\frac{4}{9}+\frac{8}{9}+\frac{12}{9}+\frac{16}{9}+...+\frac{48}{9}+\frac{52}{9}+\frac{56}{9}\)
\(=\frac{4+8+12+16+...+48+52+56}{9}\)
Xét 4 + 8 + 12 + 16 + ... + 48 + 52 + 56
Số các số hạng là:
(56 - 4) : 4 + 1 = 14 (số)
4 + 8 + 12 + 16 + ... + 48 + 52 + 56 = (56 + 4) x 14 : 2 = 420
\(\frac{4+8+12+16+...+48+52+56}{9}=\frac{420}{9}=\frac{140}{3}\)
=( 1/12+9/12+2/12+1/12) + ( 2/7+5/7) + (10/20+9/20)
= 13/12 +1+19/20
đến đây bạn tự tính nha
4/5 : 2/9 x 2/9 : 4/5
= 4/5 x 9/2 x 2/9 x 5/4
= ( 4/5 x 5/4 ) x ( 9/2 x 2/9 )
= 1x1
= 1
\(\frac{4}{5}:\frac{2}{9}\times\frac{2}{9}:\frac{4}{5}\)
\(=\frac{4}{5}\times\frac{9}{2}\times\frac{2}{9}\times\frac{5}{4}\)
\(=\left(\frac{4}{5}\times\frac{5}{4}\right)\times\left(\frac{2}{9}\times\frac{9}{2}\right)\)
\(=1\times1\)
\(=1\)
a)\(\frac{2}{3}:\frac{4}{9}+\frac{1}{3}:\frac{4}{9}\)
=\(\frac{4}{9}:\left(\frac{2}{3}+\frac{1}{3}\right)\)
=\(\frac{4}{9}:1=\frac{4}{9}\)
b
9x1=9
9x2=18
9x3=27
9x4=36
9x5=45
9x6=54
9x7=63
9x8=73
9x9=81
9x10=90
2/5+3/6=2/5+1/2=4/10+5/10=9/10
\(\frac{2}{5}+\frac{3}{6}=\frac{12}{30}+\frac{15}{30}=\frac{27}{30}=\frac{9}{10}\)
\(3+\frac{2}{5}-\frac{3}{4}\times\frac{4}{5}\)
\(=3+\frac{2}{5}-\frac{3}{4}\)
\(=\frac{3\times20+2\times4-3\times5}{20}\)
\(=\frac{60+8-15}{20}\)
\(=\frac{68-15}{20}\)
\(=\frac{53}{20}\)
\(5-\frac{7}{9}+\frac{2}{3}-\frac{5}{6}:\frac{4}{9}\)
\(=5-\frac{7}{9}+\frac{2}{3}-\frac{45}{24}\)
\(=\frac{5\times72-7\times8+2\times24-45\times3}{72}\)
\(=\frac{360-56+48-135}{72}\)
\(=\frac{217}{72}\)
= (9/5 + 6/5) + 4/9 + 8/7 + 3/2 = 3 + (100/63 + 3/2) = 389/126 + 3 = 767/126
