First we arrange the words starting with A, we fix A at extreme left position and remaining 4 letters can be arranged in 4!=24 ways. Now, placing G at first position, letters A, A, I, N can be arranged in
4!
2!
=12 ways. Similarly, words starting with I are
4!
2!
=12 ways. ∴ Total number of words obtained=24+12+12=48 The 49 th word is NAAGI. ∴50 th word will be NAAIG.