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Hi my sisters and brothers can tell me the answer because i don’t understand the question

Acircle has a circumference of 7.850 units. what is its radius?

Monitors manufactured by tsi electronics have life spans that have a normal distribution with a standard deviation of 1800 hours and a mean life span of 20,000 hours. if a monitor is selected at random, find the probability that the life span of the monitor will be more than 17,659 hours. round your answer to four decimal places.