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Hi there! Have questions about your homework? At Brainly, there are 60 million students who want to help each other learn. Questions are usually answered in less than 10 minutes. Try it for yourself by posting a question! :D

we have 5 subjects to be arranged in 6 periods such that each subject is taken at least once.So naturally one subject is to be repeated. so one the periods can be occupied in 5 different ways.now that one subject is to be repeated , another period can also be filled in 5 different ways. Now having filled two of the periods with the same subject , we have 4 subjects left . So the next period can be filled in 4 different ways.proceeding this this way, the next period can be filled in 3 ways ,the next in two ways and the last in 1 way.(this completes all 6 periods)

so the total number of possible arrangements = 5*5*4*3*2*1 = 600