Question 71920
2x+1<3x<12
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Split this into two problems.  The first problem is 
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2x + 1 < 3x
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Subtract 2x from both sides and you get:
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+1 < x
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This tells you that x must be greater than +1.
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Now let's work the second problem.  It is:
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3x < 12
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Dividing both sides by +3 results in:
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x < +4
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So on one hand, x must be greater than +1, but on the other hand x must be less than +4.
We can write this as:
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+1 < x < +4
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As a check you can select some values of x between +1 and +4 and plug them in to the original
problem.  For example, let's try x = +2. Using this value, the original problem becomes:
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2x + 1 < 3x < 12
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2(+2) + 1 < 3(+2) < 12
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4 + 1 < 6 < 12
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5 < 6 < 12
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That works ... so x = +2 works as a check.
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Hope this helps you understand how to work the problem.