Radioactive elements decay via first-order kinetics. Consider a certain type of nucleus that has a rate constant of 2. 6 x 10⁻² h⁻¹. A sample contains 6. 5 x 10⁸ radioactive nuclides. Calculate the time required for 61% of the nuclides to decompose.

On a test the graders have a mean of 77 and a standard deviation of 8. if we can approximate the distribution of these graders by a number distribution what percent of the students. a) scores higher than 77? b) should pass the test (grades > 60)? c) should fail the test (grades < 60)?