3: Tính bằng cách hợp lý:
a) 0,25 x 92, 6 + 6 ,4 x 25% + 1/4 . cứu mình!
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`a, 4/9 + 2/5 + 5/9= (4/9 +5/9) + 2/5= 1 + 2/5= 5/5 + 2/5= 7/5`
`b, 6/13 + 5/8 + 7/13=(6/13 + 7/13) + 5/8=1+5/8= 8/8 + 5/8= 13/8`
`c, 5/11 + 6/25 + 66/121 = ( 5/11 + 66/121 ) + 6/25=1 + 6/25 = 25/25 + 6/25 = 31/25`
`d, 1/2 + 1/3 + 1/4 + 1/6 + 1/12 + 1/24= (1/2 + 1/4) +(1/3 + 1/6) + (1/12 + 1/24)= 3/4 + 1/2 + 1/8= 6/8 + 4/8 + 1/8= 11/8`
`@ yl`
= 12 : (0,1 x 0,25 + 6)
= 12 : (25 + 6)
= 12 : 31
= 0.38709677419
Câu 5:
a: \(31\cdot\left(-18\right)+31\cdot\left(-81\right)-31\)
\(=31\left(-18-81-1\right)\)
\(=31\cdot\left(-100\right)=-3100\)
b: \(\left(-12\right)\cdot47+\left(-12\right)\cdot52+\left(-12\right)\)
\(=\left(-12\right)\left(47+52+1\right)\)
\(=-12\cdot100=-1200\)
c: \(13\cdot\left(23+22\right)-3\cdot\left(17+28\right)\)
\(=13\cdot45-3\cdot45\)
\(=45\cdot10=450\)
d: \(-48+48\left(-78\right)+48\left(-21\right)\)
\(=48\left(-1-78-21\right)\)
\(=48\left(-100\right)=-4800\)
Câu 4:
a: \(\left(-6-2\right)\left(-6+2\right)=\left(-8\right)\cdot\left(-4\right)=32\)
b: \(\dfrac{\left(7\cdot3-3\right)}{-6}=\dfrac{21-3}{-6}=\dfrac{18}{-6}=-3\)
c: \(\left(-5+9\right)\cdot\left(-4\right)=4\cdot\left(-4\right)=-16\)
d: \(\dfrac{72}{-6\cdot2+4}=\dfrac{72}{-12+4}=\dfrac{72}{-8}=-9\)
\(2\times3\times5+25\times8\times4+70+4\times2\times25\)
\(=15\times2+100\times8+70+100\times2\)
\(=30+800+70+200\)
\(=\left(30+70\right)+\left(800+200\right)\)
\(=100+100\times10\)
\(=100+1000\)
\(=1100\)
1 1/3 x 1 1/4 x 1 1/5 x 1 1/6 x 1 1/7 x 1 1/8 = 4/3 x 5/4 x 6/5 x 7/6 x 8/7 x 9/8 = 4x5x6x7x8x9/3x4x5x6x7x8 = 9/3 = 3
\(A=\frac{18\times123+9\times567\times2+3\times310\times6}{25\times1,8\times4}\)
\(A=\frac{18\times123+9\times2\times567+3\times6\times310}{25\times4\times1,8}\)
\(A=\frac{18\times123+18\times567+18\times310}{100\times1,8}\)
\(A=\frac{18\times\left(123+567+310\right)}{180}\)
\(A=\frac{18\times1000}{180}\)
\(A=\frac{18000}{180}\)
\(A=100\)
0,25×92,6+6,4×25%+1/4
=1/4×92,6+1/4×6,4+1/4
=1/4×(92,6+6,4+1).
=1/4×100=25.
vậy x=25
\(0,25\times92,6+6,4\times25\%+\dfrac{1}{4}\\ =\dfrac{1}{4}\times92,6+6,4\times\dfrac{1}{4}+\dfrac{1}{4}\\ =\dfrac{1}{4}\times\left(92,6+6,4+1\right)\\ =\dfrac{1}{4}\times100=25\)