What is the missing number ‘X’ of the series 7, X, 21, 31, 43?

32. Consider the following matrix:
3    8    10    2    ?    1
6    56    90    2    20    0
What is the missing number at ‘?’ in the matrix?

Find the missing number : 3, 5, 7, 11, 13, .........

2, 4, 16, 256, ––---. Which is the next number?

Find the missing number.

7,9,10,49,81,........

Find the missing number in the given series: 11, 33, 55, ……… 99.