An animal shelter spends $2.50 per day to care for each cat and $3.00 per day to care for each dog. Parker noticed that the shelter spent $46.50 caring for cats and dogs on Thursday. Parker found a record showing that there were a total of 18 cats and dogs on Thursday. How many cats were at the shelter on Thursday?

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?