Data Sufficiency

If 5 x + 3 y = 17, what is the value of x?

(1) x is a positive integer.

(2) y = 4 x.


[spoiler]Source: https://gmat.practicetests.teachstreet.com[/spoiler]

imo B

2 variable requires 2 equations

pradeepkaushal9518 wrote:imo B

2 variable requires 2 equations

Hey,

In this case, (B) is sufficient!

However, the rule 2 variables & 2 equations is NOT written in stone. It depends on case-per-case basis. Sometimes you can have 2 equations and still not be able to solve them. So just make sure you confirm that you are able to solve rather than simply look for 2 vars and 2 eq's.


Thanks!

D in my opinion..The meat of the question is to evaluate the choice A.

When the LCM of the x coeff and the y coeff added with the lowest of two is Greater than the constant, that equation has only one value..

5x+3y=17

lcm(5,3) = 15 add 3 to it...===> 18

18>17

so there is only one solution possible.

5x+3y=17

x=1 y=4
x=2 y=7/3 ( no where given that y is integer)

do u think 1 is sufficient

However, the rule 2 variables & 2 equations is NOT written in stone. It depends on case-per-case basis. Sometimes you can have 2 equations and still not be able to solve them.

We can't use the n variables and n equations tactic when:

--equations aren't linear
--equations aren't distinct (the so-called "evil-twin" situation)
--we have integers-->this restricts the kinds of values variables can take such that you may have sufficiency even if you have fewer equations than variables

In general, the risk in using the tactic is concluding INSUFFICIENCY. So be careful before you conclude a statement is insufficient when using this tactic. But when concluding SUFFICIENCY, there isn't as much risk.

--------

The question stem provides us with 1 equation and 2 unknowns. Knowing nothing about the properties of the unknowns, we would need an additional equation.

But (1) tells us x is a positive integer. But, as Pradeep showed, y can be a non-integer. It can also be a negative number:

5(4) + 3(-1) = 17

Thus, (1) is insufficient. Eliminate A and D.

(2) provides us with an additional equation. Thus, we have two equations, and two unknowns, and, without solving, we can safely and quickly conclude that (2) is sufficient by itself.

Choose B.

thanks testluv for clearing the confusion.

Testluv wrote: We can't use the n variables and n equations tactic when:

--equations aren't linear
--equations aren't distinct (the so-called "evil-twin" situation)
--we have integers-->this restricts the kinds of values variables can take such that you may have sufficiency even if you have fewer equations than variables

Hey,

Could you please clarify the third rule. I get the first 2 but unsure where you are getting at with the third one.

Thank you.