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If 7x- 4y = -1 and 5x + 3y = 52, then x-y=

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If 7x- 4y = -1 and 5x + 3y = 52, then x-y=  [#permalink]

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New post 03 Aug 2019, 23:21
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

70% (02:14) correct 30% (02:45) wrong based on 23 sessions

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Re: If 7x- 4y = -1 and 5x + 3y = 52, then x-y=  [#permalink]

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New post 04 Aug 2019, 12:14
If 7x- 4y = -1 and 5x + 3y = 52, then x-y=

[7x- 4y = -1]x3 => 21x-12y=-3
[5x + 3y = 52]x4 => 20x+12y=208

Adding both the equation
41x=205
x=5 => to find y... replace x=5 in one of the equations

[5x + 3y = 52]
3y=52-25=27
y=9

x-y=5-9=-4 = Answer A
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Re: If 7x- 4y = -1 and 5x + 3y = 52, then x-y=  [#permalink]

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New post 11 Aug 2019, 19:22
Bunuel wrote:
If 7x- 4y = -1 and 5x + 3y = 52, then x-y=

(A) -4

(B) -3

(C) 1

(D) 4

(E) 5


Multiply the first equation by 3 to obtain 21x - 12y = -3. Similarly, multiply the second equation by 4 to obtain 20x + 12y = 208. Now add the two new equations to get:

41x = 205

x = 5

Substituting 5 for x in 5x + 3y = 52, we have:

25 + 3y = 52

3y = 27

y = 9

Therefore, x - y = 5 - 9 = -4.

Answer: A
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Re: If 7x- 4y = -1 and 5x + 3y = 52, then x-y=   [#permalink] 11 Aug 2019, 19:22
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