Question

repede ex 8 si 9 in 10 min

Answer 1

8.
4+8+12+...+396=200x;
4·1+4·2+4·3+...+4·99=4·50·x;
4(1+2+3+...+99)=4·50·x |:4;
99·100/2=50·x;
99·50=50·x |:50;
99=x;
x€|N;
Din ambele rezulta ca S={99};
9. La un magazin s-au adus 120 de paini;
10 paini..........80lei;
120paini........xlei;
10/120=80/x =>x=80×120/10=80×12=
960(lei);
Raspuns: cele 120 de paini costa 960 de lei;
Sau o alta metoda:
Daca 10 paini costa 80 de lei, inseamna ca o paine costa:
80:10=8(lei);
Atunci, 120 de paini costa:
120×8=960(lei);