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a) 896 × 23 = 896 × (20 + 3)
= 896 × 20 + 896 × 3
= 17920 + 2688
= 20608
896 × 23 = 896 × (24 – 1 )
= 896 × 24 – 896 × 1
= 211504 – 896
= 20608
b) 547 × 38 = 547 × (30 + 8)
= 547 × 30 + 547 × 8
= 20786
547 × 38 = 547 × (39 – 1)
= 547 × 39 - 547 × 1
= 21333 – 547
= 20786
![](https://rs.olm.vn/images/avt/0.png?1311)
so sáng qua phân số trung gian: \(\dfrac{47}{73}\)
có
\(\dfrac{47}{70}>\dfrac{47}{73}\)
\(\dfrac{39}{73}< \dfrac{47}{73}\)
\(=>\dfrac{47}{70}>\dfrac{39}{73}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: 11/10>1>10/11
b: 4/9=44/99
c: 15/25=3/5
12/15=4/5
mà 3/5<4/5
nên 15/25<12/15
a: 11/10>1>10/11
b: 4/9=44/99
c: 15/25=3/5
12/15=4/5
mà 3/5<4/5
nên 15/25<12/15
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta thấy: \(\frac{11}{10}>1;\frac{10}{11}< 1\)
\(\Rightarrow\frac{11}{10}>\frac{10}{11}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{39}{38}>\frac{93}{94}\)
\(\frac{43}{49}< \frac{93}{94}\)
38/39 < 39/40
Ta có:
\(\frac{38}{39}=\frac{39}{39}-\frac{1}{39}=1-\frac{1}{39}\)
\(\frac{39}{40}=\frac{40}{40}-\frac{1}{40}=1-\frac{1}{40}\)
Vì \(\frac{1}{39}>\frac{1}{40}\)
=> \(1-\frac{1}{39}< 1-\frac{1}{40}\)
hay \(\frac{38}{39}< \frac{39}{40}\)