Problem Solving

VJesus12 wrote:$$y=248-398x$$ Which of the following values of x gives the greatest value of y in the equation above?

(A) 200
(B) 100
(C) 0.5
(D) 0
(E) -1

[spoiler]OA=E[/spoiler]

Source: GMAT Prep

We see that if x is negative, rather than subtracting 398x from 248, we are summing the values of 248 and |398x|. Thus, when x is -1, we can get the largest value of y.

Alternate solution:

We see that the given equation is a line with a negative slope (i.e., a line that is going down from left to right). Thus, the smaller the x-value, the larger the y-value. Therefore, when x is the smallest, y will be the largest. The smallest x-value given is -1 and it will yield the maximum y-value.

Answer: E