  Let $M$ and $M_n,n\ge1$ be nonnegative 2-by-2 matrices such that
$\lim_{n\rightarrow\infty}M_n=M.$ It is usually hard to estimate the entries of
$M_{k+1}\cdots M_{k+n}$ which are useful in many applications. In this paper,
under a mild condition, we show that up to a multiplication of some positive
constants, entries of $M_{k+1}\cdots M_{k+n}$ are asymptotically the same as
$\xi_{k+1}\cdots \xi_{k+n},$ the product of the tails of a continued fraction
which is related to the matrices $M_k,k\ge1,$ as $n\rightarrow\infty.$
