Let ∑un be a series of positive terms. Given that ∑un is convergent and also \(\mathop {\lim }\limits_{n \to \infty } \frac{{{u_{n + 1}}}}{{{u_n}}}\) exists, then the said limit is
1
Necessarily equal to 1
2
Necessarily greater than 1
3
May be equal to 1 or less than 1
4
Necessarily less than 1