Question 1118924
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A common sense solution using mental arithmetic does exactly the same thing as the algebraic solution shown by the other tutor.<br>
Comparing the solution below to that algebraic solution can help you understand how the algebra works.<br>
After the number is tripled and increased by 1, the result is between -20 and 10.  So after it was tripled but before it was increased by 1, the result was between (-20-1) = -21 and (10-1) = 9.<br>
Then, if the original number after being tripled was between -21 and 9, the original number was between (-21/3) = -7 and (9/3) = 3.<br>
Answer: the original number was between -7 and +3.