  Let $\left\lbrace F_{k}\right\rbrace_{k\geq0}$ be the Fibonacci sequence
defined by $F_{k}=F_{F-1}+F_{k-2}$ for all $ n\geq2$ with initials $F_{0}=0\;
F_{1}=1$. Let $\left\lbrace J_{n}\right\rbrace_{n\geq0}$ be the Jacobsthal
sequence defined by $J_n=2J_{n-1}+J_{n-2}$ for all $ n\geq2$ with initials
$J_0=0$, $J_1=1$. In this paper we find all the solutions of the two
Diophantine equations $J_n +J_m =F_a$ ,$F_n +F_m =J_a$ in the non-negative
integer variables (n,m,a),i.e we determine all Fibonacci numbers which are sum
of two Jacobsthal numbers, and also determine all Jacobsthal numbers which are
sum of two Fibonacci numbers.
