Question

(prima intrebare) Cate numere dau prin impartirea la 10 catul 15?
(a doua intrebare)Se da numarul x=123456789101112........25.Care este suma cifrelor lui x?

Answer 1

a)

n:10=15 rest x

n=10×15+x
n=150+x

x∈{0, 1, 2, ..., 9}
n∈{150, 151, 152, ..., 159}

n are 10 valori

b)

S=1+2+3+4+5+7+8+9+1+0+1+1+2+1+...+2+5

S=(1+2+...+9)+1×10+(1+2+...+9)+2×6+(1+2+3+4+5)

S=9×8:2+10+9×8:2+12+5×6:2

S=36+10+36+12+15

S=46+36+27

S=82+27

S=99