Bài 2 : Tính nhanh
a, 15\(\dfrac{2121}{4343}\)+15*\(\dfrac{222222}{434343}\)
b, A=\(\dfrac{2006\cdot125+1000}{126\cdot2005-888}\)
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`a)2018xx(1/2+1212/2424)`
`=2018xx(1/2+1/2)`
`=2018xx2/2=2018`
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`b)15xx2121/4343+15xx222222/434343`
`=15xx(2121/4343+222222/434343)`
`=15xx(21/43+22/43)`
`=15xx43/43=15`
Ta có :
Tử số :
( 2005 + 1 ) . 125 + 1000
2005 . 125 + 125 + 1000
2005 . 125 +1125
Mẫu Số :
( 125 + 1 ) . 2005 - 888
125 . 2005 + 2005 - 888
125 . 2005 + 1117
Ta có phân số : \(\dfrac{2005\cdot125+1125}{125\cdot2005+1117}\) = \(\dfrac{1125}{1117}\)
\(=15x\left(\dfrac{21}{43}+\dfrac{22}{43}\right)=15x1=15\)
\(\frac{\left(2005+1\right).125+1000}{\left(125+1\right).2005-888}\)
= \(\frac{2005.125+125+1000}{125.2005+2005-888}\)
= \(\frac{2005.125+1125}{125.2005+1117}\)
= \(\frac{250625+1125}{250625+1117}\)
= \(\frac{125875}{125871}\)
b. 16×25+44×100/ 29×96+142×48
=400+4×11×100/29×96+71×2×48
=400+400×11/29×96+71×96
=400×(1+11)/96×(29+71)
=400×12/96×100=1/2
\(a,=15\left(\dfrac{2121}{4343}+\dfrac{222222}{434343}\right)=15\left(\dfrac{21}{43}+\dfrac{22}{43}\right)=15\cdot1=15\)