What is a half-life? A. the amount of time it takes for 25% of a radioactive isotope sample to decay
B. half of the time it takes for an organism to die
C. the amount of time it takes for a radioactive isotope to become stable
D. the amount of time it takes for half of a radioactive isotope sample to decay

In positive numbers less than 1, the zeros between the decimal point and a non-zero number are blank significant

Two students, each riding bicycles, start from the same apartment building and ride to the same building on campus, but each takes a different route. the first student rides 1100 m due east and then turns due north and travels another 1430 m before arriving at the destination. the second student heads due north for 1930 m and then turns and heads directly toward the destination. at the turning point, how far is the second student from the destination?

How does an observation about an object differ from an inference about that object