Question

Cate numere naturale de trei cifre exista ,stiind ca prima si ultima cifra sunt identice ?

Answer 1

Avem cifrele {1,2,3,4,5,6,7,8,9}
Cu 1 : 101,111...191.-10 numere
Rezulta 10*9 cifre=90 numere se pot forma.

Answer 2

Sunt 990 numere de trei cifre în total.
Conform cerinței date,avem:
101,111,121,131,141,151,161,171,181,191.
202,212,222,232,242,252,262,272,282,292.
303,313,323,333,343,353,363,373,383,393.
404,414,424,434,444,454,464,474,484,494.
505,515,525,535,545,555,565,575,585,595.
606,616,626,636,646,656,666,676,686,696.
707,717,727,737,747,757,767,777,787,797.
808,818,828,838,848,858,868,878,888,898.
909,919,929,939,949,959,969,979,989,999.
Așadar,sunt 90 de numere.