Question

Ce valori poate lua numarul natural n stiind ca numerele 3n si 4n au impreuna 7 cifre? *rezolvare completa,puncte duble*

Answer 1

n∈N ⇒ 3n<4n ⇒ 3n are 3 cifre, iar 4n 4 cifre.
3n are 3 cifre ⇒ n∈A=N∩[100/3,999/3]={34, 35, 36, ...,333}
4n are 4 cifre ⇒ n∈B=N∩[1000/4,9999/4]={250, 251, 252, ..., 2499}
n∈A∩B={250, 251, 252, ....333}