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x + y = 90000 (1)
0.05x + 0.03y = 4040 (2)
Multiply equation (2) by 20 (both sides). Keep equation (2) as is. You will get
x + y = 90000 (1')
x + 0.6y = 80800 (2')
Now subtract equation (2') from equation (1'). You will get
0.4y = 90000 - 80800
0.4y = 9200
y = 9200/0.4 = 2300.
ANSWER. Gross sale for product B was $23000; gross sale for product A was the rest, 90000-23000 = 67000 dollars.
CHECK. 0.03*23000 + 0.05*67000 = 4040 dollars. ! Correct !
Solved.
I used the Elimination method to solve the system of equations.