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a )\(\frac{13}{15}+\frac{4}{7}-\frac{101}{105}\)
\(=\frac{91}{105}+\frac{60}{105}-\frac{101}{105}\)
\(=\frac{50}{105}\)
\(=\frac{10}{21}\)
b ) \(\frac{2}{5}+\frac{3}{5}\cdot\frac{4}{5}\)
\(=\frac{2}{5}+\frac{12}{25}\)
\(=\frac{10}{25}+\frac{12}{25}\)
\(=\frac{22}{25}\)
c )\(\frac{254\cdot399-145}{254+399\cdot253}\)
\(=\frac{253\cdot399+399-145}{254+399\cdot253}\)
\(=\frac{253\cdot399+254}{254+399\cdot253}\)
\(=1\)
d )\(\frac{5932+6001\cdot5931}{5932\cdot6001-69}\)
\(=\frac{5932+6001\cdot5931}{5931\cdot6001+6001-69}\)
\(=\frac{5932+6001\cdot5931}{5931\cdot6001+5932}\)
\(=1\)
e )\(\frac{1}{5}\div\frac{2}{7}\)
\(=\frac{1}{5}\cdot\frac{7}{2}\)
\(=\frac{7}{10}\)
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Tử = 254x399 - 399 + 399 - 145 = 253x399 + 254
Mẫu = 253x399 + 254
2: \(=\dfrac{59}{10}\cdot\dfrac{2}{3}-\left[\dfrac{7}{3}\cdot\left(4+\dfrac{1}{2}-2\right)\right]\cdot\dfrac{4}{7}\)
\(=\dfrac{59}{15}-\dfrac{4}{3}\cdot\dfrac{5}{2}=\dfrac{59}{15}-\dfrac{10}{3}=\dfrac{59-50}{15}=\dfrac{9}{15}=\dfrac{3}{5}\)
4: \(=254+254\cdot399+399\)
\(=254\cdot400+399\)
\(=101600+399=101999\)
5: \(=638+3900-41=3900+597=4497\)
\(a)\) Ta có :
\(\frac{51}{85}=\frac{3}{5}\)
\(\frac{58}{145}=\frac{2}{5}\)
Vì \(\frac{3}{5}>\frac{2}{5}\) nên \(\frac{51}{85}>\frac{58}{145}\)
Vậy \(\frac{51}{85}>\frac{58}{145}\)
\(b)\) Ta có :
\(\frac{69}{-230}=\frac{-3}{10}\)
\(\frac{-39}{143}=\frac{-3}{11}\)
Vì \(\frac{-3}{10}< \frac{-3}{11}\) nên \(\frac{69}{-230}< \frac{-39}{143}\)
Vậy \(\frac{69}{-230}< \frac{-39}{143}\)
\(c)\) Ta có :
\(1+\frac{-7}{41}=\frac{34}{41}\)
\(1+\frac{13}{-47}=\frac{34}{47}\)
Vì \(\frac{34}{41}>\frac{34}{47}\) nên \(1+\frac{-7}{41}>1+\frac{13}{-47}\) hay \(\frac{-7}{41}>\frac{13}{-47}\)
Vậy \(\frac{-7}{41}>\frac{13}{-47}\)
\(d)\) Ta có :
\(1-\frac{40}{49}=\frac{9}{49}\)
\(\frac{15}{21}=\frac{5}{7}=\frac{35}{49}< \frac{40}{49}\)
Vậy \(\frac{40}{49}>\frac{15}{21}\)
Bài1
a) 25/42 - 20/63 =5/18
b) 9/50 - 13/75 - 1/6 = -4/25
c) 2/15 - 2/65 - 4/39 = 0
Bài2
a) x + 7/12 =17/18-1/9 b) 29/30 - (18/23 + x)=7/69
x + 7/12 = 5/6 18/23 + x =29/30 - 7/69
x =5/6 - 7/12 18/23 +x = 199/230
x = 1/4 x = 199/230 - 18/23
x= 19/230
a . 254 x 399 - 145 / 254 + 399 x 253 = ( 253 + 1 ) x 399 - 145 / 254 + 399 x 253
= 253 x 399 + 1 x 399 - 145 / 254 + 399 x 253
=253 x 399 + 399 - 145 / 254 + 399 x 253
= 253 x 399 + ( 399 - 145) / 254 + 399 x 253
= 253 x 399 + 254 / 254 + 399 x 253
= 1
b. 1997 x 1996 - 995 / 1995 x 1997 + 1002 = 1997 x ( 1995 + 1 ) - 995 / 1995 x 1997 + 1002
= 1997 x 1995 + 1997 - 1995 / 1995 x 1997 + 1002
= 1997 x 1995 + ( 1997 - 995 ) / 1995 x1997 + 1002
= 1997 x1995 + 1002 / 1995 x 1997 + 1002
= 1
c. 5932 + 6001 x 5031 / 5932 x 6001 - 69 = 5932 + 6001 x 5031 / ( 5031 + 1 ) x 6001 - 69
= 5932 + 6001 x 5031 / 5031 x 6001 + 6001 - 69
= 5932 + 6001 x 5031 / 5031 x 6001 + ( 6001 - 69 )
= 5932 + 6001 x 5031 / 5031 x 6001 + 5932
= 1
d. 1995 x 1997 - 1 / 1996 x 1995 + 1994 = 1995 x ( 1996 + 1 ) - 1 / 1996 x 1995 + 1994
= 1995 x1996 + 1995 - 1 / 1996 x 1995 + 1994
= 1995 x 1996 + ( 1995 - 1 ) / 1996 x 1995 + 1994
= 1995 x 1996 + 1994 / 1996 x 1995 + 1994
= 1