Question

aflati cate nr naturale de forma 4ab sunt divizibile cu 10 dar nu sunt divizibile cu 100​

Answer 1

$\displaystyle\bf\\\boxed{\bf un~numar~este~divizibil~cu~10,~daca~ultima~sa~cifra~este~obligatoriu~0}~.\\\\\\\boxed{\bf un~numar~este~divizibil~cu~100,~daca~ultimele~doua~cifre~ale~numarului~sunt~0}~.\\\\\\\boxed{\bf un~numar~este~divizibil~cu~10^n,~daca~ultimele~n~cifre~ale~numarului~sunt~0}~.\\\\---------------------------------------\\\\\overline{4ab}~\vdots~10 \implies b=0.\\\overline{4ab}~nu~este~divizibil~cu~100 \implies a \neq 0.$$\displaystyle\bf\\a~poate~lua~9~valori,~deci~vom~avea~~\boxed{\bf 9~numere}~~cu~proprietatea~din~enunt.$