Answer:
- x + y = 9
- 5x +2y = 30
Explanation:
You are given two bits of information that relate to the numbers of items:
- the total number of items purchased
- the total cost of items purchased
These two relations let you write two equations in the two unknowns, one for each relation.
Of course, the total cost is the cost of each multiplied by the number purchased. The variables are defined as the number purchased.
_____
Though the question doesn't ask for it, the solution can be found by elimination. Subtract twice the first equation from the second:
... (5x +2y) -2(x +y) = (30) -2(9)
... 3x = 12 . . . . . simplify
... x = 4 . . . . . . . divide by 3
... 4 + y = 9 . . . . substitute the value of x into the first equation
... y = 5 . . . . . . . subtract 4
The solution is (x, y) = (4, 5).