Tính nhanh
7,8 * 1,001 *0,625
18,2 * 0,26 *0,125
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tính nhanh
7,8 x 1,001 x 0,625 cái số bên cạnh là phân số nha
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18,2 x 0,26 x 0,125
\(\dfrac{7,8\times1,001\times0,625}{18,2\times0,26\times0,125}\)
\(=\dfrac{3,9\times2\times1,001\times5\times0,125}{18,2\times2\times0,13\times0,125}\)
\(=\dfrac{3,9\times10,01\times0,125}{36,4\times0,13\times0,125}\)
\(=\dfrac{3,9\times77}{36,4}\)
\(=\dfrac{33}{4}\).
S= 1+0,5+0,25+0,125+0,0625+0,03125
S=1+1/2+1/4+1/8+1/16+1/32
2S=2+1+1/2+1/4+1/8+1/16
2S-S= (2+1+1/2+1/4+1/8+1/16) - (1+1/2+1/4+1/8+1/16+1/32)
S= 2-1+1-1/2+1/2-1/4+1/4-1/8+1/8-1/16+1/16-1/32
S=2 - 1/32
S= 63/32
Bài 1: Ta có: \(4\dfrac{3}{5}+\dfrac{7}{10}< X< \dfrac{20}{3}\)
\(\dfrac{23}{5}+\dfrac{7}{10}< X< \dfrac{20}{3}\)
\(\dfrac{138}{30}< X< \dfrac{200}{3}\)
\(\Rightarrow X\in\left\{\dfrac{160}{30};\dfrac{161}{30};\dfrac{162}{30};...;\dfrac{198}{30};\dfrac{199}{30}\right\}\)
Bài 2: \(X-2019\dfrac{2}{13}=3\dfrac{7}{26}+4\dfrac{7}{52}\)
\(\Rightarrow X-\dfrac{26249}{13}=\dfrac{85}{26}+\dfrac{215}{52}\)
\(\Rightarrow X-\dfrac{26249}{13}=\dfrac{385}{52}\)
\(\Rightarrow X=\dfrac{105381}{52}\)
\(\frac{1}{2}:0,5-\frac{1}{4}:\frac{26}{100}+\frac{1}{8}:\frac{1}{8}-\frac{1}{10}:\frac{1}{10}\)
\(=1-\frac{25}{26}+1-1\)\(=\frac{1}{26}\)
=2347,8- 7,8:(0,04-0,005-0,025)
=2347,8-7,8:0.01
=2347,8-0.078
=2347,722
\(a,7,8:2x=\frac{1}{4}:2\frac{2}{3}\)
\(7,8:2x=\frac{3}{32}\)
\(2x=7,8:\frac{3}{32}\)
\(2x=\frac{416}{5}\)
\(x=\frac{416}{5}:2\)
\(x=\frac{208}{5}\)
\(b,0,25x:3=\frac{5}{6}:0,125\)
\(0,25x:3=\frac{20}{3}\)
\(0,25x=\frac{20}{3}\times3\)
\(0,25x=20\)
\(x=20:0,25\)
\(x=80\)
\(\frac{7,8\times1,001\times0,625}{18,2\times0,26\times0,125}=\frac{30\times0,26\times1,001\times0,125\times5}{18,2\times0,26\times0,125}=\frac{30\times5\times1,001}{18,2}=\frac{150,15}{18,2}=8,25\)
\(\frac{7,8.1,001.0,625}{18,2.0,26.0,125}=\frac{7,8.3,85.0,26.0,125.5}{\frac{7}{3}.7,8.0,26.0,125}=\frac{3,85.5}{\frac{7}{3}}=\frac{\frac{77}{4}}{\frac{7}{3}}=\frac{77}{4}:\frac{7}{3}=\frac{33}{4}=8,25\)