Find expected value of compound Poisson process

Question

We have compound Poisson process with $\lambda = 3$ and jumps $D_{j}$ of size $1$ or $2$, where $P \{ D_{i} = 1 \} = 0.25$. Find mean value of this process in $t = 10$.

Mean value of compound Poisson process is equal $\lambda tE(D_{1})$. $E(D_{1}) = 1 \cdot 0.25 = 0.25$ (Im not sure in this point).

So, mean value of this process equals $3 \cdot 20 \cdot 0.25 = 15$???

Answer 1

$E(D_{1}) = 1 \cdot 0.25 + 2 \cdot 0.25 = 0.75$.

Expected value $= 3 \cdot 20 \cdot 0.75 = 45$