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Several students are singing in a line. Amy is the fourth one from the left. From the right, Amy is the fourth too. How many students are singing? (adapted from $$2019$$ Math kangaroo Problems, Level $$1-2$$, Question \#$$5$$) 
Overseas Competition->Knowledge Point->Word Problem Modules->Applying Addition and Subtraction
It comes $4+4=8$ when we count Amy twice.  The number of all singing students is $4+4-1=7$ 