An inlet pipe can fill a water tank in 10 hours, while an outlet pipe can empty the same tank in 15 hours. By mistake both pipes are left open. How long will it take to fill the water tank with both pipes open?

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Is the number 128.439 a rational number

The computer that controls a bank's automatic teller machine crashes a mean of 0.6 times per day. what is the probability that, in any seven-day week, the computer will crash less than 5 times? round your answer to four decimal places