` 5/7 xx 4 = 20/7`
` 4/7 + 5/21 = 12/21 + 5/21 = 17/21`
` 4/3 - 1 = 4/3 - 3/3 = 1/3`
` 7/2 : 3 = 7/2 xx 1/3 = 7/6`
`7800 : 100 + 56 xx 14`
` = 78 + 784`
` = 862`
`x - 5/6 = 1/2`
` x = 1/2 + 5/6`
` x = 4/3`
a) Tính
`5/7 xx 4 =20/7 `
`4/7 +5/21 = 12/21 + 5/21 =17/21`
`4/3 - 1 = 4/3 -3/3 =1/3`
`7/2: 3 = 7/2 xx 1/3 = 7/6`
B)`7800:100 + 56 xx14 `
`=78 + 56 xx14`
`=78 + 784`
`=862`
\(x=\dfrac{1}{2}+\dfrac{5}{6}=\dfrac{3}{6}+\dfrac{5}{6}=\dfrac{8}{6}=\dfrac{4}{3}\)
`5/7xx4=20/7`
`4/3-1=4/3-3/3=1/3`
`4/7+5/21=12/21+5/21=17/21`
`7/2:3=7/2xx1/3=7/6`
`7800:100+56xx14`
`=78+784`
`=862`
`x-5/6=1/2`
`x=1/2+5/6`
`x=3/6+5/6`
`x=8/6`
`x=4/3`
a) Tính:
\(\dfrac{5}{7}\times4=\dfrac{5}{7}\times\dfrac{4}{1}=\dfrac{5\times4}{7\times1}=\dfrac{20}{7}\)
\(\dfrac{4}{3}-1=\dfrac{4}{3}-\dfrac{1}{1}=\dfrac{4\times1}{3\times1}-\dfrac{1\times3}{1\times3}=\dfrac{4}{3}-\dfrac{3}{3}=\dfrac{4-3}{3}=\dfrac{1}{3}\)
\(\dfrac{4}{7}+\dfrac{5}{21}=\dfrac{4\times3}{7\times3}+\dfrac{5}{21}=\dfrac{12}{21}+\dfrac{5}{21}=\dfrac{12+5}{21}=\dfrac{17}{21}\)
\(\dfrac{7}{2}:3=\dfrac{7}{2}:\dfrac{3}{1}=\dfrac{7}{2}\times\dfrac{1}{3}=\dfrac{7\times1}{2\times3}=\dfrac{7}{6}\)
b) Tính giá trị biểu thức:
7800 : 100 + 56 x 14
= ( 7800 : 100 ) + ( 56 x 14 )
= 78 + 784
= 862
\(x-\dfrac{5}{6}=\dfrac{1}{2}\)
\(x=\dfrac{1}{2}+\dfrac{5}{6}\)
\(x=\dfrac{4}{3}.\)