[tex]\rm \overline{abcd}= \overline{dcba} \Rightarrow a=d~si~b=c. \\ \\ Numarul~"a"~poate~avea~9 ~valori.~(1,2,3,4,5,6,7,8,9). \\ Numarul~"b"~poate~avea~10~valori.~(0,1,2,3,4,5,6,7,8,9). \\ \\ Deoarece~a=d~si~b=c,~rezulta~ca~numerele~\overline{abcd}~sunt~de~forma~ \overline{abba}.[/tex]
[tex]\rm Iar~cum~a~poate~lua~9~valori,~iar~b~poate~lua~10~valori,~rezulta~ca~ \\ exista~9 \cdot 10=90~de~numere~cu~proprietatea~din~enunt.[/tex]
