Solution :
E1 : Event that first drawn ball is red, second is blue and so on.
E2 : Event that first drawn ball is blue, second is red and so on.
∴ P(E_1) = 4\over 8 \times 4\over 7 \times 3\over 6 \times 3\over 5 and
\therefore P(E_2) = 4\over 8 \times 4\over 7 \times 3\over 6 \times 3\over 5
P(E) = P(E_1) + P(E_2) = 2 \times 4\over 8 \times 4\over 7 \times 3\over 6 \times 3\over 5 = 6\over 35