Tính hợp lí
1. 453 . (-27) . 27 . 253
2. 34. ( 66 - 5 ) . 66 . ( 34 + 5 )
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1: =66+34-73-27+99=99
2: =54-45+30-54-30+5=-40
3: =42-56+33-33+56-42=0
4: =50-47-50+18+47-18=0
5: =10-28+30-4=2-4+10=12-4=8
\(\text{1.-(-66)+34+(-73)-27+99}.\)
\(=66+34-73-27+99=100-100+99=-99.\)
\(\text{2.54-(45-30+54)-30+5}.\)
\(54-45+30-54-30+5=\left(54-54\right)+\left(-45+5\right)+\left(30-30\right)=-40.\)
\(\text{3.42-56+33-(33-56+42)}.\)
\(=42-56+33-33+56-42=\left(42-42\right)+\left(-56+56\right)+\left(33-33\right)=0.\)
\(\text{4.50-(47+50-18)+(47-18)}.\)
\(=50-47-50+18+47-18=\left(50-50\right)+\left(-47+47\right)+\left(18-18\right)=0.\)
\(\text{5.10-(28-30+4)}.\)
\(=10-28+30-4=10+30-20-8-4=20-12=8.\)
\(\text{6.-(-73)+(44-94+27)+94}.\)
\(=73+44-94+27+94=\left(73+27\right)+\left(-94+94\right)+44=100+44=144.\)
a) 27 + 34 + 66 = 27 + (34 + 66) = 27 + 100 = 127 | b) 7 x 5 x 2 = 7 x (5 x 2) = 7 x 10 = 70 |
Ta có 34.(66 - 5) - 66.(34 + 5)
= 34.66 - 34.5 - 66.34 - 66.5
= -5.(34 + 66)
= - 5.100 = - 500
34(66-5)-66(34+5)=34.66-34.5-34.66-66.5=(34.66-34.66)-5(34+66)=-500
a) \(48.19+48.15+134.52\)
\(=48\left(19+15\right)+6968\)
\(=48.34+6968\)
\(=1632+6968\)
\(=8600.\)
b) \(27.121-87.27+73.34\)
\(=27\left(121-87\right)+73.34\)
\(=27.34+73.34\)
\(=34\left(27+73\right)\)
\(=34.100\)
\(=3400.\)
c) \(125.98-125.46-52-25\)
\(=125\left(98-46\right)-52-25\)
\(=125.52-52-25\)
\(=52\left(125-1\right)-25\)
\(=52.124-25\)
\(=6448-25\)
\(=6423.\)
d) \(136.23+136.17-40.36\)
\(=136\left(23+17\right)-40.36\)
\(=136.40-40.36\)
\(=40\left(136-36\right)\)
\(=40.100\)
\(=4000.\)
e) \(66.25+5.66+66.14+33.94\)
\(=33\left(2.50+5.2+14.2+94\right)\)
\(=33\left(50+10+28+94\right)\)
\(=33.182\)
\(=6006.\)
a , 27 . ( 58 - 43 ) + 43 . ( 27 + 58 ) b . 66 . ( 34 - 75 ) - 34 . ( 66 + 75 )
= 27 . 10 + 43 . 85 = 66 . ( 34 - 75 ) + ( -34 ) . ( 66 + 75 )
= 270 + 3755 = [ 66 . 75 + 66 + 75 ] . 34 . ( - 34 )
= 4025 0
k và kb nếu có thể
= 66 + 34 -73 - 27 + 99
= 100 - (73+27) + 99
=100 - 100 + 99 = 99