Is (10,20,30,40,...) an arithmetic progression?

Correct answer: Yes, common difference is (10)

The governing concept is the definition of an arithmetic progression: the difference between every pair of consecutive terms must be constant. For this sequence, 20 − 10 = 10, 30 − 20 = 10, and 40 − 30 = 10. Since the same difference occurs each time, the sequence is an arithmetic progression with common difference d = 10. Thus, option A is correct. Option B incorrectly uses 20, which is a term rather than the difference between consecutive terms. Option C is wrong because an arithmetic progression does not require all terms to be equal; it requires their differences to be equal. Option D is wrong because the sequence increases, rather than decreases. The repeated difference provides the decisive test.