Radon is a colorless gas that is naturally released by rocks and soils and may concentrate in tightly closed houses. because radon is slightly radioactive, there is some concern that it may be a health hazard. radon detectors are sold to homeowners worried about this risk, but the detectors may be inaccurate. university researchers placed 12 randomly selected detectors in a chamber where they were exposed to 105 pico curies per liter of radon over 3 days. here are the readings given by the detectors: 91.9 97.8 111.4 122.3 105.4 95.0 103.8 99.6 96.6 119.3 104.8 101.7

assume that you know that the standard deviation of readings for detectors of this type is o = 9. (yates, moore & mccabe, the practice of statistics, p.555) is there significant evidence at the 10% level that the mean reading differs from the true value of 105?