What is (d) in the sequence (2.2,3.1,4.0,4.9,\ldots)?

Correct answer: (0.9)

The common difference of an arithmetic progression is the fixed amount added to one term to obtain the next term. It is found by subtracting any term from the term immediately after it. In this sequence, the numbers rise regularly, so the same difference should appear between every pair of consecutive terms. This is the central idea behind identifying an AP and its common difference.

Subtract the first term from the second: \(3.1-2.2=0.9\). Checking the next pair gives \(4.0-3.1=0.9\), and the following pair gives \(4.9-4.0=0.9\). Thus the fixed common difference is \(d=0.9\), so option C follows. Options 0.7, 0.8, and 1.1 do not match the consecutive gaps.