We know that, the odd numbers are $ \{1,3,5,7,9\} $ $\therefore n(a)=5$ Divisible by $3$ are $\{0,3,6,9\}, n(b)=4$ Even numbers are $\{0,2,4,6,8\}, n(c)=5$ and prime numbers are $\{2,3,5,7\}, n(d)=4$ $\therefore$ Four-digit numbers $abcd$ exist $=5 \cdot 4 \cdot 5 \cdot 4$ $=400$