A. Number of words using 4 letters out of 6 letters =6P4=2!6!=6×5×4×3 =360
B. Number of words using all letters =6P6=6 ! =720
C. Number of words starting with vowel = Number of ways of choosing first letter ( out of O and
A) × Number of ways of arranging 5 alphabets =2×5!=2×120=240