123, 98, 82, 73, 69, ?

Select the number from among the given options that can replace the question mark (?) in the following series.
123, 98, 82, 73, 69, ?

Option
a) 49
b) 68
c) 52
d) 57

Solution

123, 98, 82, 73, 69, ?
Difference between numbers:
-25, -16, -9, -4
5², 4², 3², 2²,
Next will be 1² = 1
69 – 1 = 68

Answer: b) 68