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\(\dfrac{1}{10}+\dfrac{1}{2}:0,5-\dfrac{1}{4}:0,25+\dfrac{1}{8}:0,125\)
\(=\dfrac{1}{10}+\dfrac{1}{2}\times2-\dfrac{1}{4}\times4+\dfrac{1}{8}\times8\)
\(=\dfrac{1}{10}+1-1+1\)
\(=\dfrac{1}{10}+1=\dfrac{1}{10}+\dfrac{10}{10}=\dfrac{11}{10}\)
13, 25 : 0, 5 + 13, 25 : 0, 25 + 13, 25 : 0, 125
= 13, 25 . 2 + 13, 25 . 4 + 13, 25 . 8
= 13, 25 . ( 2 + 4 + 8 )
= 13, 25 . 14
= 185, 5
ính bằng cách thuận tiện nhất:
0.5 x 17 x 5 + 0.25 x 520 + 31 x 2.5
=>2,5x17+2.5x52+2,5x31
=2,5(17+52+31)
=2,5x100
=250
\(0,5\times17\times5\times0,25\times520+31\times2,5\)
\(\Rightarrow2,5\times17+2,5\times52+2,5\times31\)
\(\Rightarrow2,5\times\left(17+52+31\right)\)
\(\Rightarrow2,5\times100\)
\(\Rightarrow2500\)
2021 x 2021 - 2019 x 2023
= (2019 +2) x ( 2023 -2) - 2019 x 2023
= 2019 x 2023 - 2 x 2019 + 2 x 2023 - 4 - 2019 x 2023
= ( 2019 x 2023 - 2019 x 2023) + 2 x ( 2023 - 2019) - 4
= 0 + 2 x 4 - 4
= 8 - 4
= 4
2021 x 2021 - 2019 x 2023
= (2019 +2) x ( 2023 -2) - 2019 x 2023
= 2019 x 2023 - 2 x 2019 + 2 x 2023 - 4 - 2019 x 2023
= ( 2019 x 2023 - 2019 x 2023) + 2 x ( 2023 - 2019) - 4
= 0 + 2 x 4 - 4
= 8 - 4
= 4
0,6 × 7 + 1,2 × 45 + 1,8
= 0,6 × 7 + 0,6 × 2 × 45 + 0,6 × 3
= 0.6 × 7 + 0,6 × 90 + 0,6 × 3
= 0,6 × ( 7 + 90 + 3 )
= 0,6 × 100
= 60
Lời giải:
$2\times A=\frac{2}{1\times 3}+\frac{2}{3\times 5}+\frac{2}{5\times 7}+...+\frac{2}{19\times 21}$
$2\times A=\frac{3-1}{1\times 3}+\frac{5-3}{3\times 5}+\frac{7-5}{5\times 7}+...+\frac{21-19}{19\times 21}$
$=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+....+\frac{1}{19}-\frac{1}{21}$
$=1-\frac{1}{21}=\frac{20}{21}$
$\Rightarrow A=\frac{20}{21}: 2= \frac{10}{21}$
12 , 35 : 0 , 5 + 12 , 35 : 0 , 25 + 12 , 35 : 0 , 125
= 12 , 35 x 2 + 12 , 35 x 4 + 12 , 35 x 8
= 12 , 35 x ( 2 + 8 ) + 12 , 35 x 4
= 12 , 35 x 10 + 49 , 4
= 123 , 5 + 49 , 4
= 172 , 9
Tk mk nha !!!
12,35 : 0,5 + 12,35 : 0,25 + 12,35 : 0,125 = 12,35 x 2 + 12,35 x 4 + 12,35 x 8
= 12,35 x ( 2 + 4 + 8 )
= 12,35 x 14
= 172,9