Each student in a physics lab is assigned to find the location where a bright object may be placed in order that a concave mirror with radius of curvature r = 40cm will produce an image three times the size of the object. Two students complete the assignment at different times using identical equipment, but when they compare notes later, they discover that their answers for the object distance are not the same. Explain why they do not necessarily need to repeat the lab, and justify your response with a calculation.