Question 302365
One number is 4 more than another, and their sum is 60. What is the smaller number? If x=the larger number and y=smaller number, then which of the following systems could be used to solve the problem?  
x+y=60 and -x+y=4; 
x+y=60 and x-y=4 or 
x+y=60 and x+y=4
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Try each of the 3 pairs, see which one works.