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If y = 4x + 10 and y = 7x – 5, what is the value of y?

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If y = 4x + 10 and y = 7x – 5, what is the value of y? [#permalink]  23 Jun 2018, 11:45
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Question Stats:

100% (00:36) correct 0% (00:00) wrong based on 4 sessions
If $$y = 4x + 10$$ and $$y = 7x - 5$$, what is the value of y?

[Reveal] Spoiler: OA
30

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Sandy
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VP
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Re: If y = 4x + 10 and y = 7x – 5, what is the value of y? [#permalink]  01 Jul 2018, 21:48
sandy wrote:
If $$y = 4x + 10$$ and $$y = 7x - 5$$, what is the value of y?

[Reveal] Spoiler: OA
30

Here;

Let us multiply equation 1 with 7 = $$(y = 4x + 10) * 7$$ = $$7y = 28x + 70$$

multiply equation 2 with 4 = $$(y = 7x - 5) * 4$$ = $$4y = 28x - 20$$

Now subtracting both equation,
$$7y = 28x + 70$$
$$4y = 28x - 20$$
(-)_______________________

$$3y = 90$$
or $$y = 30$$
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Retired Moderator
Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 171

Kudos [?]: 2911 [0], given: 394

Re: If y = 4x + 10 and y = 7x – 5, what is the value of y? [#permalink]  16 Jul 2018, 06:59
Expert's post
Explanation

Since each equation is already solved for y, set the right side of each equation equal to the other.

$$4x + 10 = 7x - 5$$

$$10 = 3x - 5$$

$$15 = 3x$$

$$5 = x$$

Substitute 5 for x in the first equation and solve for y.

$$y = 4(5) + 10$$

$$y = 30$$

x = 5 and y = 30. Be sure to answer for y, not x.
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Sandy
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Re: If y = 4x + 10 and y = 7x – 5, what is the value of y?   [#permalink] 16 Jul 2018, 06:59
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