tính bằng cách thuận tiện nhất : 1/4 chia 25% - 1/8 : 0,125 + 1/2 - 1/10 :10%
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A,
20,19 x 111- 20,19:0,1- 2019
= 20,19x ( 111+ 10 - 1 )
=20,19 x 120
=2422,8
B,
1/100 -1/2 : 50% + 1/4 : 25% - 1/8 : 0,125 + 1999 : 1999
= 0,01 - 0,5 : 0,5 + 0,25 : 0,25 - 0,125 : 0,125 + 1
= 0,01 - 1 + 1 - 1 +1
= 0,01+ ( 1+1 - 1- 1 )
=0,01

\(\dfrac{1}{4}:0,25-\dfrac{1}{8}:0,125+\dfrac{1}{2}:0,5-\dfrac{1}{16}:0,0625\\ =0,25:0,25-0,125:0,125+0,5:0,5-0,0625:0,0625\\ =1-1+1-1\\ =0+1-1\\ =1-1\\ =0\)

\(\dfrac{1}{10}+\dfrac{2}{10}+\dfrac{3}{10}+\dfrac{4}{10}+\dfrac{5}{10}+\dfrac{6}{10}+\dfrac{7}{10}+\dfrac{8}{10}+\dfrac{9}{10}\)
\(=\left(\dfrac{1}{10}+\dfrac{9}{10}\right)+\left(\dfrac{2}{10}+\dfrac{8}{10}\right)+\left(\dfrac{3}{10}+\dfrac{7}{10}\right)+\left(\dfrac{4}{10}+\dfrac{6}{10}\right)+\dfrac{5}{10}\)
\(=1+1+1+1+\dfrac{5}{10}\)
\(=4+\dfrac{5}{10}\)
\(=\dfrac{45}{10}\)
\(13,25:0,5+13,25:0,25+13,25:0,125+13,25\times6\)
\(=13,25:\dfrac{1}{2}+13,25:\dfrac{1}{4}+13,25:\dfrac{1}{8}+13,25\times6\)
\(=13,25\times2+13,25\times4+13,25\times8+13,25\times6\)
\(=13,25\times\left(2+4+8+6\right)\)
\(=13,25\times20\)
\(=265\)

Tính thuận tiện:
a, 46 : 24 + 8 : 24
= (46 + 8) : 24
= 54 : 24
= \(\dfrac{9}{4}\)
b, 705 : 45 - 336 : 45
= (705 - 336): 45
= 369 : 45
= \(\dfrac{41}{5}\)
c, 2345 : 12,5 : 8
= 2345 : (12,5 x 8)
= 2345 : 100
= 2,345

\(\dfrac{1}{4}\) : 0,25 - \(\dfrac{1}{8}\) : 0,125 + \(\dfrac{1}{2}\) : 0,5 - 1
= 0,25 x 4 - 0,125 x 8 + 0,5 x 2 - 1
= 1 - 1 + 1 - 1
= 0 + 1 - 1
= 1 - 1
= 0
A = \(\dfrac{1}{4}\) : 0,25 - \(\dfrac{1}{8}\): 0,125 + \(\dfrac{1}{2}\): 0,5 - 1
A = \(\dfrac{1}{4}\) x 4 - \(\dfrac{1}{8}\) x 8 + \(\dfrac{1}{2}\) x 2 - 1
A = 1 - 1 + 1 - 1
A = (1 - 1) + (1 - 1)
A = 0

.............(Đề bài)...............
=1/2*2/5+1/5*1/2+1/2*2/5
=(1/2+1/2)+(2/5+1/5+2/5)
=1+1
=2
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