2005 AMC 12A Problem 2

Attempt Problem 2 of the 2005 AMC 12A below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2005 AMC 12A solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

2.

The equations 2x+7=32x + 7 = 3 and bx−10=−2bx - 10 = -2 have the same solution for x.x. What is the value of b?b?
−8-8
−4-4
−2-2
44
88
Answer: B
Concepts:linear equationsubstitution
Small hint:
First solve 2x+7=32x + 7 = 3 for xx
Big hint:
Substitute that value of xx into bx−10=−2bx - 10 = -2
Solution:
Solving 2x+7=32x + 7 = 3 gives x=−2.x = -2.
Substituting into the second equation, −2b−10=−2,-2b - 10 = -2, so −2b=8-2b = 8 and b=−4.b = -4.
Thus, the correct answer is B.
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