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Ý bạn là \(\frac{7}{6}\) : \(\frac{1}{0.06}\) - 3 % à?
Nếu vậy thì giải như sau:
= 7/6 : 1/0.06 - 3/100
= 7/6 : 100/6 - 3/100
= 7/100 - 3/100
= 4/100 = 1/25
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E= 6/7:1/0,21-10%
E=6/7 * 0,21-1/10
E=9/50-1/10
E=2/25
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\(\frac{1}{7}< \frac{x}{13}< \frac{2}{7}\)
\(\frac{1\times13}{7\times13}< \frac{x\times7}{13\times7}< \frac{2\times13}{7\times13}\)
\(\frac{13}{91}< \frac{x7}{91}< \frac{26}{91}\)
\(\Rightarrow13< x7< 26\)
Vì \(x7⋮7\) mà \(13< x7< 26\Rightarrow x7=14;21\)
\(\Rightarrow x=14\div7=2\)
\(x=21\div7=3\)
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Tổng của các số trong mỗi ô nhỏ là 26
6 + 8 + 7 + 5 = 26
8 + 8 + 6 + 4 = 26
10 + 9 + 4 + 3 = 26
Vậy số cần tìm là: 10
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nhận thấy :
2 + 5 - 1 = 6
6 + 1 - 5 = 2
8 + 2 - 9 = 1
=> 7 + 3 - ? = 2
=> ?=8
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= 1/6 -1/7 + 1/7 -1/8 + ....+1/80 - 1/81
= 1/6 -1/81
= 25/162
\(\frac{1}{6\times7}+\frac{1}{7\times8}+...+\frac{1}{80\times81}\)
\(=\)\(\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{80}-\frac{1}{81}\)
\(=\)\(\frac{1}{6}-\frac{1}{81}\)
\(=\)\(\frac{75}{486}\)
\(=\)\(\frac{25}{162}\)