Question

"calcule X e Y:
a)x/y=3/4 sendo x+y=21

Answer 1

a)

 x    =    3
-----      ----
  y          4

4x = 3y
4x - 3y = 0
x + y = 21      (3)

4x - 3y = 0
3x + 3y = 63 (+)
----------------------
7x = 63
x = 63/7
x = 9

x + y = 21
9 + y = 21
y = 21 - 9
y = 12
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b)
 x      =   y
------      ---- 
  2           3

3x = 2y

3x - 2y = 0
x + y = 40   (2)

3x - 2y = 0
2x + 2y = 80 (+)
---------------------
5x = 80
x = 80/5
x = 16

x + y = 40
16 + y = 40
y = 40 - 16
y = 24

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c)

 x      =    5
-----       ------
  y            4

4x = 5y

4x - 5y = 0  
x + y = 18     (5)

4x - 5y = 0
5x + 5y = 90  (+)
--------------------------
9x = 90
x = 90/9
x = 10

x + y = 18
10 + y = 18
y = 18 - 10
y = 8

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