Q.
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Start your 14-day free trial to unlock the full solution →The key idea is to treat the compound inequality as two separate inequalities and solve for by isolating it through algebraic operations. The solution set is , or .
Concept and Intuition
A compound inequality like means that the expression lies between 7 and 11, inclusive. To find the range of , we need to "undo" the operations applied to — first the division by 2, then the addition of 11, and finally the multiplication by 3 — but we must do this to all three parts of the inequality simultaneously. This preserves the relationship: whatever we do to the middle, we do to the left and right ends.
The core principle: linear inequalities behave like equations when adding, subtracting, multiplying, or dividing by a positive number. The only twist is that multiplying or dividing by a negative number flips the inequality signs — but here, all operations involve positive numbers, so no flipping occurs.
A common mistake is to multiply only the middle term by 2, forgetting to multiply the 7 and 11 as well. Always apply the same operation to all three parts of a compound inequality.
Step-by-Step Solution
- Write the compound inequality clearly We have:
- Eliminate the denominator Multiply every part of the inequality by 2 (a positive number, so inequality signs stay the same):
This simplifies to:
- Isolate the term with Subtract 11 from all three parts (again, no sign change):
Which gives:
- Solve for …
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