Tính bằng cách thuận tiện
A) 1/3x 1/2 + 1/2 x 1/5
B) 1/3 x 1/2 - 1/5 x 1/2
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a) 2/3 : 3/5 × 5/7 : 2/3
= 2/3 × 5/3 × 5/7 × 3/2
= 25/21
b) 1 1/2 × 1 1/3 × 1 1/18 × 1 1/15 × 1 1/24 × 1 1/35
= 3/2 × 4/3 × 19/18 × 16/15 × 25/24 × 36/35
= 2 × 152/35 × 15/14
= 304/35 × 15/14
= 152/7
a: =8/15x1/4=2/15
b: \(=\dfrac{5}{3}\cdot\dfrac{4}{5}\cdot\dfrac{6}{7}=\dfrac{24}{21}=\dfrac{8}{7}\)
c: \(=\dfrac{2}{5}\left(\dfrac{3}{7}+\dfrac{4}{7}\right)=\dfrac{2}{5}\)
(1-1/2)×(1-1/3)×(1-1/4)×(1-1/5)×1-1/6=1/2×2/3×3/4×4/5×5/6=1/6
\(a.\left(\dfrac{2}{5}.\dfrac{5}{2}\right).\dfrac{10}{21}=1.\dfrac{10}{21}=\dfrac{10}{21}\)
\(\dfrac{1}{2}.4+\dfrac{3}{4}.4=2+3=5\)
\(=\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot\dfrac{3}{4}\cdot\dfrac{4}{5}\\ =\dfrac{1}{5}\)
`1/3xx 1/2 + 1/2 xx 1/5`
`=1/2 xx (1/3 +1/5)`
`= 1/2 xx ( 5/15 +3/15)`
`= 1/2 xx 8/15`
`= 8/30`
`=4/15`
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`1/3 xx 1/2 - 1/5 xx 1/2`
`= 1/2 xx (1/3 -1/5)`
`= 1/2 xx ( 5/15 -3/15)`
`=1/2 xx 2/15`
`= 2/30`
`=1/15`
a)
`1/3xx1/2+1/2xx1/5`
`=1/2xx(1/3+1/5)`
`=1/2xx(5/15+3/15)`
`=1/2xx8/15`
`=4/15`
b)
`1/3xx1/2-1/5xx1/2`
`=1/2xx(1/3-1/5)`
`=1/2xx(5/15-3/15)`
`=1/2xx2/15`
`=1/15`