Răspuns:
Explicație pas cu pas:
3*10^n - 2^n*5^n-1 = 30*10^n-1 - 2*10^n-1 = 10^n-1 (30 - 2) = 28*10^n-1
10^n*7 = 70*10^n-1
28*10^n-1 / 70*10^n-1 = 28/70 = 4/10 = 2/5
