Question 94907
Think about this ...
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If you start adding the numbers from -22 to zero, you are adding -22, - 21, - 20, -19 and
so on up to adding -3, then -2, then -1. 
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To this total you begin to add the numbers on the positive side of zero starting with +1,
then +2, +3 and so on....
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When you think about it the -1 cancels the +1, the -2 cancels the +2, the -3 cancels the
+3 and so on until you get to -19 cancels +19, -20 cancels + 20, -21 cancels the +21, and
-22 cancels +22.  So when you add all the integers from -22 to +22 the total is zero.
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Starting at that point you next add +23 then +24 and then +25. The total of these three
integers is 72 as required by the problem.  
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So +25 is the last integer you need and, therefore, it is the x you are looking for.
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Algebraically adding all the integers from -22 to +25 results in a total of +72.
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Hope this gives you some insight into how you can solve this problem mostly by just thinking
about it logically.