a sample of a radioactive isotope decays from 60 mg to 45 mg over the course of 75 days. How long will it take for the sample to decay to 65% of the original amount

Which of the following units is not an official si unit

Did the detergents containing enzymes work better at removing stains than those containing no enzyme? why or why not?

Which of the following statements is true about both nuclear fusion and nuclear fission? they occur in the sun. heavy atoms are split. two light nuclei combine. some mass changes into energy.