A Board examination question reads as follows: "An object is placed at a distance of 12 cm in front of a concave mirror. It forms a real image four times larger than the object. Calculate the distance of the image from the mirror." In the key, the answer was v = -48 cm, taking that m = -4. But in the question, it is stated that the image is four times larger than the object, which implies that the image is five times the size of the object, which implies that m = -5, which implies that v = -60 cm. How are we to interpret this question, m = -4 or m = -5 and why?

(Vicky Iyer)

The question is to be interpreted as m = -4. Hence the answer given in the key is correct.