3. The half-life of carbon-14 is about 5600 years. A
fossil with 1/4 the normal
proportion of C, is
probably
years
old.

A. 2,800
B. 11,200
C. 22,400

In an experiment examining the effects tai chi on arthritis pain, callahan (2010) selected a large sample of individuals with doctor-diagnosed arthritis. half of the participants immediately began a tai chi course and the other half (the control group) waited 8 weeks before beginning. at the end of 8 weeks, the individuals who had experienced tai chi had less arthritis pain that those who had not participated in the course.