The average of nine number is 50. The average of first five numbers is 54 and that of the last three numbers is 52. Then the sixth number is :

Average of 9 numbers = 50
Hence sum of 9 numbers = 450
Average of last three numbers = 52
Hence sum of them will be = 156
Average of first five numbers is = 54
Hence sum of them will be = 54 × 5 = 270
So 6^th number will be = sum of 9 numbers - (sum of first five numbers + sum of last three numbers)
= 450 - (156 + 270)
= 24