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=>( y - 1/2 )+( y - 1/6 )+...+( y- 1/90 ) = 1
=>y + y+.. + y - 1/2 - 1/6-...- 1/90 = 1
=>y + y+..+ y - 1/(1x2) - 1/(2x3) - 1/(3x4)-...- 1/(9x10) = 1
=> 9y -( 2-1)/(1x2) - (3-2)/(2x3)-...- (10-9)/(9x10) = 1
=>9y- 2/(1x2) + 1(1x2) - 3/(2x3) + 2/(2x3)-...- 10/(9x10) + 9(9x10) = 1
=> 9y- 1 + 1/2 - 1/2 + 1/3-...- 1/9 + 1/10 = 1
=>9y- 1 + 1/10 = 1
=> 9y- 9/10 =1
=>y=19/90
Vậy y=19/90
a) y = 5/14 : 6/7
y = 5/12
vậy y = 5/12
b) y = 4/9 x 2/3
y = 8/27
vậy t = 8/27
c) y = 1/2 - 3/10
y = 1/5
vậy y = 1/5
d) y = 5/6 - 1/3
y = 1/2
vậy y = 1/2
Ta có: ( y + 1 ) + ( y + 2 ) + ( y + 3 ) + ........ + ( y + 9 )=90
=> 90=(y+y+......+y)+(1+2+3+....+9)
=> 90=9y+[(9+1)x9:2]
=> 90=9y+90:2
=> 9y=90-45
=> y=45:9
=> y=5
Ta có: ( y + 1 ) + ( y + 2 ) + ( y + 3 ) + ........ + ( y + 9 ) = 90
<=> (y + y + ...... + y) + (1 + 2 + 3 +....+ 9) = 90
<=> 9y + [(9 + 1) x 9 : 2]
<=> 9y + 90 : 2 = 90
<=> 9y + 45 = 90
<=> 9y = 90 - 45
=> y = 45:9
Vậy y=5
168-9*y=1+2+3+4+5+6+7+8+9
168-9*y=45
9*y=648-45
9*y=603
y=603/9
y=67
5/7 x y= 2/3
y = 2/3 : 5/7
y = 14/15
2/9 + y=1+2/3
2/9 + y= 5/3
y = 5/3 - 2/9
y = 13/9
a) y + 3/7 x 21/9 = 5
y + 3/7 x 7/3 = 5
y + 1 = 5
y = 4
b) y x 3/5 - 1/2 = 4/5
y x 3/5 = 4/5 + 1/2
y x 3/5 = 13/10
y = 13/6
c) 9/8 - y + 2/5 = 1/4
y - 2/5 = 9 /8 - 1/4
y - 2/5 = 7/8
y = 51/40
d) y - 6/5 : 2/3 = 5/6
y - 9/5 = 5/6
y = 79/30
e) y : 7/8 + 3/4 = 7/4
y : 7/8 = 1
y = 7/8
(y+1)+(y+2)+...+(y+9)=90
=>9y+(1+2+...+9)=90
=>9y+45=90
=>y+5=10
=>y=5