7

$2x + 1 > 10$

$2x > 9$

$x > 4.5$

The answer in the book says: $x\lt 4.5$.

Am I doing it wrong?

amWhy
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Akshat
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    Given the problem you have written, your answer is correct. – Paul Sundheim Aug 29 '14 at 14:20
  • You are doing fine! The book must be wrong here. – drhab Aug 29 '14 at 14:20
  • Be aware that answers in textbooks (particularly for lower-division undergraduate courses and earlier in the educational journey) are the product of many hands, and no one -- not even the author -- checks all the answers compiled. A first edition can have an error rate of 1 - 2% , and later editions can still harbor around $ \ \frac{1}{4} \ $ to $ \ \frac{1}{2} \ $ percent errors among the answers. (In your case, this could be an answer to an earlier version of the problem, or a simple typo.) – colormegone Aug 29 '14 at 14:41
  • All right, thanks everyone. :) – Always Learning Forever Aug 29 '14 at 14:48

1 Answers1

9

$$2x+1>10 \iff x\gt 4.5$$

In other words, your solution to the posted inequality is correct!

I suspect the book's (wrong) solution must be a typo/misprint, either in the solution, or in the book's statement of the problem.

The book's solution satisfies the following inequality $$-2x + 1 \gt 10 \iff -2x \gt 9 \iff x\lt -4.5,$$ but does not satisfy the posted inequality. (Plug in, say $1<4.5$ into the original inequality and test it for yourself: Certainly, claiming that $2(1) + 1 = 3\gt 10$ is absurd.)

amWhy
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