The projection lens in a certain projector is a single thin lens. an object 23.7 mm high is to be projected so that its image fills a screen 1.71 m high. the lens-to-screen distance is 3.04 m. determine the focal length of the lens.

Consider a file currently consisting of 200 blocks. assume that the file control block (and the index block in the case of indexed allocation) is already in memory. calculate how many disk i/o operations are required for contiguous, linked, and indexed (single-level) allocation strategies, for each of the conditions listed below. in the contiguous-allocation case, assume that there is not room to grow at the beginning but there is room to grow at the end. also assume that the block information to be added is stored in memory.