ISEE Mathematics Achievement Question 14: Answer and Explanation
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Question: 14
14. If 3x + 2y = 8 and 2x + y = 12, what is 5x + 3y?
- A. –20
- B. –8
- C. 16
- D. 20
Correct Answer: D
Explanation:
D
Multiply both sides of the second equation by –2: –4x –2y = –24. Stack the two equations on top of one another and combine like terms: –x = –16. Multiply both sides by –1: x = 16. Substitute 16 for x in either equation: 2(16) + y = 12. Combine like terms: y = –20. Finally, substitute the values for x and y in the expression and solve: 5(16) + (3)(–20) 80 – 60 = 20.
Rather than solve the variables individually, stack the initial equations and combine like terms: 5x + 3y = 20. The question is asking for the value of 5x + 3y, so you are done.