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There are oranges, apricots and peaches in a big basket. How many fruits are there in the basket if the peaches and the apricots together are 18, the oranges and the apricots together are 28 and 30 fruits are not apricots? 
Overseas Competition->Knowledge Point->Word Problem Modules->Unitary Method Problems->Unitary Method with Two Variables
If we sum up the number of A and P, the result is 18.  But if we sum up A and O, result is 28 instead.  Hence, there must be 10 more O than P.  Note that there are a total of 30 I and P.  Therefore, there are (30+10)/2 = 20 Oranges.  Total = 20+18=38. 