Question 307537
"cost of 4 boxes of small paper clips and 9 boxes of large paper clips is $15.75" ___ 4s + 9L = 15.75 ___ 8s + 18L = 31.50


"Eight boxes of small clips and 7 boxes of large ones cost $16.65" ___ 8s + 7L = 16.65


subtracting equations ___ 11L = 14.85 ___ L = 1.35


substituting ___ 4s + 9(1.35) = 15.75 ___ 4s = 3.60 ___ s = .90



the "trick" is to get one set of coefficients to have the same value by multiplying (sometimes both equations) 
___ then "cancel" the variable by subtracting