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Ta có:
A = [15 x (1-1/7-1/12-1/98)] / [ 18 x (1-1/7-1/12-1/98)]
= 15/18 = 5/6
\(A=\frac{15\left(1-\frac{1}{7}-\frac{1}{12}-\frac{1}{98}\right)}{18\left(1-\frac{1}{7}-\frac{1}{12}-\frac{1}{98}\right)}=\frac{15}{18}=\frac{15:3}{18:3}=\frac{5}{6}\)
k cho mk nha

`1)1/2:2/3 .... 2/3 : 1/2`
`=>1/2xx3/2 .... 2/3xx2`
`=>3/4 .... 4/3`
Vì `3/4 < 1` và `4/3>1`
`=>3/4<4/3`
__
`4/7:2/5 ... 4/7 : 3/5`
`=>4/7xx5/2....4/7xx5/3`
`=>20/14...20/21`
`=>10/7...20/21`
Vì `10/7>1` và `20/21<1`
`=>10/7>20/21`
__
`4/15:4/7....2/5xx10/3`
`=>4/15xx7/4...20/15`
`=>7/15...20/15`
Vì `7<20` nên `7/15<20/15`
__
`5/6...15/18-11/18`
`=>5/6...4/18`
Ta có : MSC : `18`
`5/6 = 15/18`
Vì `15>4` nên `5/6 > 4/18`

\(\frac{1}{15}+\frac{4}{15}+\frac{5}{18}+\frac{7}{18}\)
\(=\left(\frac{1}{15}+\frac{4}{15}\right)+\left(\frac{5}{18}+\frac{7}{18}\right)\)
\(=\frac{5}{15}+\frac{12}{18}\)
\(=\frac{1}{3}+\frac{2}{3}\)
\(=\frac{3}{3}=1\)
\(\frac{1}{15}+\frac{4}{15}+\frac{5}{18}+\frac{7}{18}\)
\(=\left(\frac{1}{15}+\frac{4}{15}\right)+\left(\frac{5}{18}+\frac{7}{18}\right)\)
\(=\frac{1}{3}+\frac{2}{3}\)
\(=1\)

1) \(\frac{1}{12}+\frac{1}{16}+\frac{3}{4}\)
\(=\frac{4}{48}+\frac{3}{48}+\frac{36}{48}\)
\(=\frac{4+3+36}{48}\)
\(=\frac{43}{48}\)
2) a) \(\frac{1}{15}+\frac{4}{15}+\frac{5}{18}+\frac{7}{18}\)
\(=\left(\frac{1}{15}+\frac{4}{15}\right)+\left(\frac{5}{18}+\frac{7}{18}\right)\)
\(=\frac{1}{3}+\frac{2}{3}=1\)
b) \(\frac{1}{8}+\frac{1}{12}+\frac{3}{8}+\frac{5}{12}\)
\(=\left(\frac{1}{8}+\frac{3}{8}\right)+\left(\frac{1}{12}+\frac{5}{12}\right)\)
\(=\frac{1}{2}+\frac{1}{2}=1\)

14/15:7/5-8/15
=14/15x5/7-8/15
=2/3-8/15
=10/15-8/15
=2/15
Chọn A nha bạn

a ) \(\frac{1}{15}+\frac{4}{15}+\frac{5}{18}+\frac{7}{18}\)
\(=\left(\frac{1}{15}+\frac{4}{15}\right)+\left(\frac{5}{18}+\frac{7}{18}\right)\)
\(=\frac{1}{3}+\frac{2}{3}\)
\(=1\)
b ) \(\frac{1}{8}+\frac{1}{12}+\frac{3}{8}+\frac{5}{12}\)
\(=\left(\frac{1}{8}+\frac{3}{8}\right)+\left(\frac{1}{12}+\frac{5}{12}\right)\)
\(=\frac{1}{2}+\frac{1}{2}\)
\(=1\)
a, \(\frac{1}{15}\)+ \(\frac{4}{15}\)+ \(\frac{5}{18}\)+ \(\frac{7}{18}\)= ( \(\frac{1}{15}\)+ \(\frac{4}{15}\)) + ( \(\frac{5}{18}\)+ \(\frac{7}{18}\))
= \(\frac{1}{3}\)+ \(\frac{2}{3}\)
= \(\frac{3}{3}\)= 1
b,\(\frac{1}{8}\)+ \(\frac{1}{12}\)+ \(\frac{3}{8}\)+ \(\frac{5}{12}\)= ( \(\frac{1}{8}\)+ \(\frac{3}{8}\)) + ( \(\frac{1}{12}\)+ \(\frac{5}{12}\))
= \(\frac{1}{2}\)+ \(\frac{1}{2}\)
= \(\frac{2}{2}\)= 1

A) 3/7 + 4/9 + 4/7 + 5/9 = ( 4/9+5/9) + ( 3/7 + 4/7) = 1+ 1 = 2
B) 1/5 + 4/11 + 4/5 + 7/11 = ( 4/11 + 7/11) + ( 1/5 + 4/5) = 1+1=2
C) 1/15 + 4/15 + 5/18 + 7/18= ( 1/15+4/15) + (5/18+7/15)= 5/15 + 12/15 = 17/15
D) 1/8 + 1/12 + 3/8 + 5/12 = (1/8 + 3/8) + ( 1/12 + 1/12) = 4/8 + 2/12 = 64/96
K nha

1/3 + 7/5 = 26/15
3/15 + 2/5 = 3/5
4/6 + 18/27 = 4/3
15/25 + 6/21 = 31/35
k nhé:))
\(\frac{1}{3}\)+\(\frac{7}{5}\)=\(\frac{5}{15}\)+\(\frac{21}{15}\)=\(\frac{26}{15}\)
\(\frac{3}{15}\)+\(\frac{2}{5}\)=\(\frac{1}{5}\)+\(\frac{2}{5}\)=\(\frac{3}{5}\)
\(\frac{4}{6}\)+\(\frac{18}{27}\)=\(\frac{2}{3}\)+\(\frac{2}{3}\)=\(\frac{4}{3}\)
\(\frac{15}{25}\)+\(\frac{6}{21}\)=\(\frac{3}{5}\)+\(\frac{2}{7}\)=\(\frac{21}{35}\)+\(\frac{10}{35}\)=\(\frac{31}{35}\)
đây nha
1/3 + 3/2
= 2/6 + 9/6
= 11/6
\(\frac{1}{15}+\frac{4}{15}+\frac{5}{18}+\frac{7}{18}\)
\(=\left(\frac{1}{15}+\frac{4}{15}\right)+\left(\frac{5}{18}+\frac{7}{18}\right)\)
\(=\frac{5}{15}+\frac{12}{18}\)
\(=\frac13+\frac23\)
\(=\frac33=1\)