Solve by plugging in numbers

[Rastis]

If y is not equal to 4, x is not equal to 0, and (y^2 - 16)/3x = (y - 4)/6, then in terms of x, y equals:

a) (x + 8)/2

b) (x - 8)/2

c) -3x/2

d) (-3x + 8)/2

e) (3x - 8)/2

[[email protected]]

Hi Rastis,

When TESTing VALUES in these types of situations, you should look for a way to make some of the math as easy as possible. This means that you might NOT end up TESTing small values.

Here, I'm going to choose a value for Y that will make the right side of the equation equal 1:

Y = 10

(Y^2 - 16)/3X = (Y - 4)/6

(100-16)/3X = (10-4)/6

84/3X = 6/6

84/3X = 1

X = 28

Now, we'll plug 28 into the answers; we're looking for an answer that equals 10.

A: (28+8)/2 = 18
B: (28-8)/2 = 10
C: -84/2 = -41
D:: -76/2 = -38
E: 76/2 = 38

Final Answer: B

GMAT assassins aren't born, they're made,
Rich

[GMATGuruNY]

If y is not equal to 4, x is not equal to 0, and (y^2 - 16)/3x = (y - 4)/6, then in terms of x, y equals:

a) (x + 8)/2

b) (x - 8)/2

c) -3x/2

d) (-3x + 8)/2

e) (3x - 8)/2

Let y=0.
Substituting y=0 into (y² - 16)/3x = (y-4)/6, we get:
-16/3x = -4/6
-16/3x = -2/3
-48 = -6x
x=8.

The question stem asks for the value of y=0. This is our target.
Now plug x=8 into the answers to see which yields our target of 0.
Only B works:
(x-8)/2 = (8-8)/2 = 0.

The correct answer is B.

[Rastis]

Thanks, Rich. I knew to plug in values but I was plugging values for both Y and X instead of plugging in for just one variable and using small values, which resulting in a huge mess. It also makes sense to make one side equal to one.

Jesse

[[email protected]]

Hi Jesse,

Here we're dealing with an equation, which means that you can TEST some of the variables randomly (choose whatever numbers you'd like), BUT you'll have to calculate the others. Since the Y showed up twice and the X showed up just once, I opted to choose a value for the Y - doing so leaves me with one variable and one equation, so I can easily solve for X.

GMAT assassins aren't born, they're made,
Rich