Șapte prieteni au obținut ca punctaj la Olimpiada de matematică doar numere naturale nenule și cel puțin doi dintre ei au primit note diferite. Știind că suma punctajelor este 49, aflați care este cel mai mare divizor comun al notelor obținute la olimpiadă de cei șapte copii.

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?