Which of the following numbers will replace the question mark (?) in the given series?
45,65,90,125,180, ? 

Correct option is B

Given:

45,65,90,125,180, ? 

Logic: differences between the consecutive terms

Number is increasing from 20,25,35,55

65 - 45 = 20

90 - 65 = 25

125 - 90 = 35

180 - 125 = 55

These differences do not immediately suggest a simple arithmetic or geometric progression Let's look at the differences of the differences:

25 - 20 = 5

35 - 25 = 10

55−35=20

the next difference would be  double of 20 = 40

Adding this new difference to the last term in our first-level differences 

55+40=95 

we add this difference to the last term in the original series to find the missing number:

180+95=275

Thus, correct option is (b)