Răspuns :
numerele suntde forma
13k+8
100≤13k+8≤999
92≤13k≤991
92/13≤k≤991/13 si k∈N
7,07..≤k≤76,2.. si k∈N
deci
k∈{8;9;....76}
in total 76-8+1=69 numere
extra de la 8*13+8=112
din 13 in 13
pan la 76*13+8=996
13k+8
100≤13k+8≤999
92≤13k≤991
92/13≤k≤991/13 si k∈N
7,07..≤k≤76,2.. si k∈N
deci
k∈{8;9;....76}
in total 76-8+1=69 numere
extra de la 8*13+8=112
din 13 in 13
pan la 76*13+8=996
___ ___
100 ≤ M₁₃+8 = abc ≤ 999 ⇒ 100:13≈7,69 adica abc =13*8+8 =112
___
999:13≈76,84 deci abc=13*76+8=996
___
⇒ abc = {13*8+8=112; 13*9+8=125; ... ; 13*76+8=996}
avem 76 -8+1= 69 numere
100 ≤ M₁₃+8 = abc ≤ 999 ⇒ 100:13≈7,69 adica abc =13*8+8 =112
___
999:13≈76,84 deci abc=13*76+8=996
___
⇒ abc = {13*8+8=112; 13*9+8=125; ... ; 13*76+8=996}
avem 76 -8+1= 69 numere