Folosind notatiile (a, b) pentru cel mai mare divizor comun si [a, b] pentru cel mai mic multiplu comun al numerelor a si b, probati re;atoa a*b = (a, b)*[a, b], penru fiecare dintre perechile de numere naturale, urmatoare: a) 15 si 20; b) 27 si 36; c)54 si 72

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?