Question

1) Cate numere de forma ab (in baza 10) exista?
2) Cate numere pare de forma ab (in baza 10) exista?
3) Cate numere de forma abc sunt divizibile cu 7?

Answer 1

   
[tex]\displaystyle \\ 1)~10;~11;\hdots 99 ~~~n = 99-10+1= \boxed{90} \\ \\ 2)~10;~12;\hdots 98 ~~~n = \frac{98-10}{2}+1= \frac{88}{2}+1=44+1=\boxed{45} \\ \\ 3)~105;~\hdots 994 ~~~n = \frac{994-105}{7}+1= \frac{889}{7}+1=127+1=\boxed{128} [/tex]