2
algebra

If 3x+4y=203x + 4y = 20 and x−2y=10x - 2y = 10, what is x+yx + y?

A

5

B

8

C

7

D

6

Correct Answer: C

Choice Bhoice C is the correct answer.

  1. Solve System: Multiply 2nd eq by 2: 2x−4y=202x - 4y = 20
  2. Add to 1st: (3x+4y)+(2x−4y)=20+20→5x=40→x=8(3x + 4y) + (2x - 4y) = 20 + 20 \rightarrow 5x = 40 \rightarrow x = 8
  3. Find y: 8−2y=10→−2y=2→y=−18 - 2y = 10 \rightarrow -2y = 2 \rightarrow y = -1
  4. Calculate: x+y=8+(−1)=7x + y = 8 + (-1) = 7

Choice Bhoice A is incorrect because calculation error.

Choice Bhoice C is incorrect because calculation error.

Choice Bhoice D is incorrect because calculation error.

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Linear Functions Set 39