2002 AMC 10B Problem 12

Attempt Problem 12 of the 2002 AMC 10B 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 2002 AMC 10B solutions, or check the answer key.

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12.

For which of the following values of kk does the equation x1x2=xkx6\dfrac{x - 1}{x - 2} = \dfrac{x - k}{x - 6} have no solution for x?x?

11

22

33

44

55

Answer: E
Concepts:rational equationlinear equation
Difficulty rating: 1370
Solution:

Cross multiplying gives (x1)(x6)=(x2)(xk),(x - 1)(x - 6) = (x - 2)(x - k), which expands to x27x+6=x2(2+k)x+2k. \begin{aligned} x^2 - 7x + 6 &= x^2 - (2 + k)x \\ &\quad {}+ 2k. \end{aligned}

Cancelling x2x^2 leaves (k5)x=2k6.(k - 5)x = 2k - 6. For each listed value k=1,2,3,4,k=1,2,3,4, this gives a valid value of xx that is neither excluded denominator value 22 nor 6.6. For k=5,k=5, the equation instead becomes 0x=4,0\cdot x=4, which has no solution.

Thus, the correct answer is E.

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