tính bằng cách thuận tiện nhất
a, 20,23 x 21 + 20,23 x 80 - 20,23
b, 5/13 x 7/11 + 5/13 x 2/11 + 8/13 x 9/11
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Lời giải:
$2,5\times 20,23\times 8\times 5=2,5\times 20,23\times 4\times 2\times 5$
$=(2,5\times 4)\times 20,23\times (2\times 5)$
$=10\times 20,23\times 10=20,23\times 100=2023$
20,23 \(\times\) 37 - 2,3 \(\times\) 5,5 + 20,23 \(\times\) 63 - 2,3 \(\times\) 4,5
= ( 20,23 \(\times\) 37 + 20,23 \(\times\) 63 ) - ( 2,3 \(\times\) 5,5 + 2,3 \(\times\) 4,5)
= 20,23 \(\times\) ( 37 + 63) - 2,3 \(\times\) ( 5,5 + 4,5)
= 20,23 \(\times\) 100 - 2,3 \(\times\) 10
= 2023 - 23
= 2000
a: \(20,23\cdot7,5+20,23+20,23+20,23:2\)
\(=20,23\cdot7,5+20,23\cdot2+20,23\cdot0,5\)
\(=20,23\left(7,5+2+0,5\right)\)
\(=20,23\cdot10=202,3\)
b: \(100:9-79,3:9\)
\(=\left(100-79,3\right):9\)
\(=20,7:9=2,3\)
a, = \(\frac{11}{21}\)x \(\left(\frac{7}{4}+\frac{5}{4}\right)\)
= \(\frac{11}{21}\)x 3
= \(\frac{33}{21}\)
b) = \(\left(\frac{23}{14}-\frac{9}{14}\right)\)x \(\frac{6}{13}\)
= 1 x \(\frac{6}{13}\)
= \(\frac{6}{13}\)
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20,23 : 0,25 + 20,23 : 0,1 + 20,23 + 85 x 20,23
= 20,23 x 4 + 20,23 x 10 + 20,23 x 1 + 85 x 20,23
= 20,23 x (4 + 10 + 1 + 85)
= 20,23 x 100
= 2023
20,23 : 0,25 + 20,23 : 0,1 + 20,23 + 85 x 20,23
= 20,23 x 4 + 20,23 x 10 + 20,23 + 85 x 20,23
= 20,23 x ( 4 + 10 + 1 + 85 )
= 20,23 x 100
= 2023
13/19 x 23/11 - 13/19 x 8/11 - 13/19 x 4/11
= 13/19 x (23/11 - 8/11 - 4/11)
= 13/19 x 1
= 13/19
\(\dfrac{13}{19}\times\dfrac{23}{11}-\dfrac{13}{19}\times\dfrac{8}{11}-\dfrac{13}{19}\times\dfrac{4}{11}\\ =\dfrac{13}{19}\times\left(\dfrac{23}{11}-\dfrac{8}{11}-\dfrac{4}{11}\right)\\ =\dfrac{13}{19}\times1=\dfrac{13}{19}\)
21/11 x 22/17x68/63
= 7x3x2x11x4x17 / 11x17x7x3x3
=8/3
5/14x7/13x26/25
=5x7x26 / 14x13x25
= 5x7x13x2 / 7x2x13x5x5
=1/5
\(\dfrac{5}{13}\times\dfrac{7}{11}+\dfrac{5}{13}\times\dfrac{2}{11}+\dfrac{8}{13}\times\dfrac{9}{11}\)
\(=\dfrac{5}{13}\times\left(\dfrac{7}{11}+\dfrac{2}{11}\right)+\dfrac{8}{13}\times\dfrac{9}{11}\)
\(=\dfrac{5}{13}\times\dfrac{9}{11}+\dfrac{8}{13}\times\dfrac{9}{11}\)
\(=\dfrac{9}{11}\times\left(\dfrac{5}{13}+\dfrac{8}{13}\right)\)
\(=\dfrac{9}{11}\times1\)
\(=\dfrac{9}{11}\)
a) \(20,23\times21+20,23\times80-20,23\)
\(=20,23\times\left(21+80-1\right)\)
\(=20,23\times100\)
\(=2023\)