Acertain element has a half life of 4.5 billion years. a. you find a rock containing a mixture of the element and lead. you determine that 60% of the original element remains; the other 40% decayed into lead. how old is the rock? b. analysis of another rock shows that it contains 5% of its original element; the other 95% decayed into lead. how old is the rock?

Aresearch study is studying the effects of a new drug for osteoporosis alzheimer's disease (ad) for women above the age of 65 years. a group of individuals with osteoporosis is randomized into two groups. one group is treated conventionally, and the second group is treated with the new medication. assessments are made at 3, 6, 12, 36, and 48 months. the conventionally treated group is assessed for ad using a serum blood test, and the treatment group is assessed for ad using a pet radiotracer that binds to beta-amyloid plaques. in comparing these 2 trial arms, the authors of the study may encounter which type of bias? a. selection bias on the risk of developing b. measurement bias c. confounding bias d. recall bias e. lead-time bias