Question

calculati ultima cifra a numerelor:
5¹⁹⁹⁹+7²°°°
3¹⁹⁹²+4¹⁹⁹⁴+5¹⁹⁹⁶+6¹⁹⁹⁸+7²°°°

Answer 1

U(n) ultima cifra a nr. n
5 la 1999 are U (5 la 1999) = 5
7 la 2000 are U(7 la 2000) = 9
U (5 la 1999 + 7 la 2000) = U(5 + 9) = 4.

3 la 1992 are U(3 la 1992) = 9
4 la 1994 are U(4 la 1994) = 6
5 la 1996 are U(5 la 1996) = 5
6 la 1998 are U(6 la 1998) = 6
7 la 2000 are U(7 la 2000) = 9
U (3 la 1992 + 4 la 1994 + 5 la 1996 + 6 la 1998 + 7 la 2000) =
= U(9 + 6 + 5 + 6 + 9) = 5.