Nickel-63 has half-life of about 96 years. after 336 years, about how many milligrams of an 800 mg sample will remain?
a)14 mg
b)71 mg
c)229 mg
d)656 mg

Assume that there is a 11% rate of disk drive failure in a year. a. if all your computer data is stored on a hard disk drive with a copy stored on a second hard disk drive, what is the probability that during a year, you can avoid catastrophe with at least one working drive? b. if copies of all your computer data are stored on four independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?