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A) 12,6 + 13,5 + 14,4 - 4,5 - 3,6 - 5,4
= ( 12,6 - 3,6 ) + ( 13,5 - 4,5 ) + ( 14,4 - 5,4 )
= 9 + 9 + 9
= 9 x 3 = 27
B) 0,2 x 17 x 7 + 0,14 x 520 + 31 x 1,4
= ( 0,2 x 7 ) x 17 + ( 0,14 x 10 ) x 52 + 31 x 1,4
= 1,4 x 17 + 1,4 x 52 + 31 x 1,4
= 1,4 x ( 17 + 52 + 31 )
= 1,4 x 100
= 140
1.Tìm X:
a) `x : 8 = 107,8 - 29,25`
`x:8=78,55`
`x=78,55xx8`
`x=628,4`
b) `x + 16,7 = 50,5 : 2,5`
`x+16,7=20,2`
`x=20,2-16,7`
`x=3,5`
2.Tìm X:
a) `x - 2,35 = 3,6 : 4,5`
`x-2,35=0,8`
`x=0,8+2,35`
`x=3,15`
b) `189,5 - x = 7,2 xx 14`
`189,5 - x = 100,8`
`x=189,5-100,8`
`x=88,7`
3. Tính giá trị biểu thức :
`13,5 : 4,5 xx 2,4 + (156,9 – 80,6) `
`=3xx2,4+76,3`
`=7,2+76,3`
`=83,5`
4. Tính giá trị biểu thức :
`1,25 xx 4,2 + 119,6 : 5,2 – 23,19`
`=5,25+23-23,19`
`=5,06`
5. Tính giá trị biểu thức :
`14,75 – 7,15 : 5 + 2,6 xx 3,5`
`=14,75 – 1,43 + 9,1`
`=22,42`
6. Tính nhanh
a) `3,6 xx 78 + 78 xx 6,4=78xx(3,6+6,4)=78xx10=780`
b) `80 xx 5,29 xx 1,25=(80xx1,25)xx5,29=100xx5,29=529`
a) \(x+\frac{1}{5}-\frac{2}{7}=4\frac{1}{2}\)
=> \(x+\frac{1}{5}-\frac{2}{7}=\frac{9}{2}\)
=> \(x=\frac{9}{2}+\frac{2}{7}-\frac{1}{5}=\frac{321}{70}\)
b) \(1\frac{3}{4}+x-\frac{7}{8}=5\)
=> \(\frac{7}{4}+x-\frac{7}{8}=5\)
=> \(\frac{7}{4}+x=\frac{47}{8}\)
=> \(x=\frac{33}{8}\)
c) \(\frac{1}{2}-\frac{1}{3}\cdot x=\frac{3}{4}\)
=> \(\frac{1}{3}\cdot x=\frac{1}{2}-\frac{3}{4}=-\frac{1}{4}\)
=> \(x=\left(-\frac{1}{4}\right):\frac{1}{3}=\left(-\frac{1}{4}\right)\cdot3=-\frac{3}{4}\)
\(A=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}+\frac{1}{128}\)
\(2\times A=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}\)
\(2\times A-A=\left(1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}\right)-\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}+\frac{1}{128}\right)\)
\(A=1-\frac{1}{128}\)
\(A=\frac{127}{128}\)
\(B=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}\)
\(2\times B=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}\)
\(B=1-\frac{1}{16}=\frac{15}{16}\)
\(\left(x+\frac{1}{2}\right)+\left(x+\frac{1}{4}\right)+\left(x+\frac{1}{8}\right)+\left(x+\frac{1}{16}\right)=1\)
\(\Leftrightarrow4\times x+\frac{15}{16}=1\)
\(\Leftrightarrow4\times x=\frac{1}{16}\)
\(\Leftrightarrow x=\frac{1}{64}\)
2A=1+1/2+1/4+1/8+.........+1/512
2A-A=(1+1/2+1/4+1/8+....+1/512)-(1/2+1/4+1/8+.....+1/1024)
A=1-1/1024
A=1023/1024
vậy A=1023/1024
a 720
b 27
c191/64=2,984375