Consider the following equation:
2x + 3y = 30.
If x and y are nonnegative integers, the following solutions are possible:
x=15, y=0
x=12, y=2
x=9, y=4
x=6, y=6
x=3, y=8
x=0, y=10
Notice the following:
The value of x changes in increments of 3 (the coefficient for y).
The value of y changes in increments of 2 (the coefficient for x).
This pattern will be exhibited by any fully reduced equation that has two variables constrained to nonnegative integers.
Bunuel
A hardware store purchased x identical standard flashlights at $5 each and y identical deluxe flashlights at $7 each. The total cost to the store for both types of flashlights was $92. What is the ratio of x to y ?
A. 5 to 7
B. 7 to 5
C. 5 to 1
D. 17 to 1
E. It cannot be determined from the information given.
5x + 7y = 92
Since 7*6 = 42, one possible solution will be yielded if 5x=50, as follows:
Case 1: x=10, y=6
As noted above:
x may change only in increments of 7 (the coefficient for y)
y may change only in increments of 5 (the coefficient for x)
Thus, two other cases are possible:
Case 2: x=10+7=17, y=6-5 = 1 --> x=17, y=1
Case 3: x=10-7=3, y=6+5 = 11 --> x=3, y=11
Since Cases 1, 2 and 3 will yield different values for x/y, the ratio of x to y cannot be determined.
For more practice with the approach used here, check my solutions for the following problems:
https://gmatclub.com/forum/eunice-sold- ... 02-20.htmlhttps://gmatclub.com/forum/for-how-many ... 91382.htmlhttps://gmatclub.com/forum/joanna-bough ... 43-20.html