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(1-2+3-4+5-6+7-8+...+101-102+103) * x-120=2012
[ -1 + ( -1 ) ... ( -1 ) + 103] * x -120 = 2012
( -1 x 51 + 103 ) * x - 120 = 2012
( -51 +103) * x = 2012 + 120
52 * x =2132
x= 2132 : 52
x= 41
Đặt A=1x3+3x5+5x7+7x9+...+99x101
6A=6x(1x3+3x5+5x7+7x9+...+99x101)
6A=1x3x6+3x5x6+5x7x6+7x9x6+...+99x101x6
6A=1x3x(5+1)+3x5x(7-1)+5x7x(9-3)+7x9x(11-5)+...+99x101x(103-97)
6A=1x3x5+1x3+3x5x7-3x5+5x7x9-3x5x7+7x9x11-5x7x9+...+99x101x103-99x101x97
6A=3+99x101x103
=>A=\(\frac{\text{3+99x101x103}}{6}\)
a)
\(\dfrac{1}{2}=0,5;\dfrac{3}{4}=0,75;\dfrac{7}{5}=1,4;\dfrac{9}{8}=1,125;\dfrac{26}{25}=1,04;\dfrac{120}{125}=0,96\)
b)
\(\dfrac{15}{25}=0,6;\dfrac{75}{25}=3;\dfrac{90}{300}=0,3;\dfrac{27}{36}=0,75;\dfrac{51}{85}=0,6\)
a,1/2=5/10;3/4=75/100;7/5=140/100;26/25=108/100;120/125=960/1000
b,15/25=60/100;75/25=300/100;90/300=3/10;27/36=3/4=75/100;
51/85=3/5=60/100;39/65=3/5=60/100
1) 25 + 91 + 75 + 101
= (25+75) + (91 + 101)
= 100 + 192
= 292
2) 41 x 39 - 41 x 9
= 41 x (39 - 9)
= 41 x 30
= 1230
3) 710 x 99 + 710
= 710 x 99 + 710 x 1
= 710 x (99 + 1)
= 710 x 100
= 71000
4) 17 x 85 + 15 x 17 - 120
= 17 x (85 + 15) - 120
= 17 x 100 -120
= 1700 -120
= 1580
5) (39 x 42 - 37 x 42) : 42
= 42 x (39 - 37) : 42
= 42 x 2 : 42
= 84 : 42
=2
6) 120 - 48 - 52
= 120 - (48 + 52)
= 120 - 100
= 20
7) 23 x 75 + 25 x 23 + 180
= 23 x (75 + 25) +180
= 23 x (75 + 25) +180
= 23 x 100 + 180
= 2300 +180
=2480
8) 2448 : [119 - (23 - 6)]
= 2448 : (119 - 17)
= 2448 : 102
= 24