In the word RAINBOW how many words are there in which A is always before I and I is always before O?
a)840
b)420
c)720
d)none of these

please explain the method clearly

• Arranging other 4 letters(R,N,B,W) in 7 places.
  7p4 = 840
  The remaining 3 letters (A,I,O) can be arranged only in 1 way.
  So total ways are 840*1= 840 ....... option a)
• 12 years agoHelpfull: Yes(2) No(5)