Problem #21: Jaws

A seaside resort along the Pacific Ocean is equipped with an electronic shark detection system which sounds an alarm on the average of 1 day out of 30. There are 10 times more false alarms than there are undetected sharks. We also know that only three out of four sharks are detected. Given the above information, what is the percentage of "peaceful" resort days if that term is defined as days unmarred by alarms or sharks?
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