If (3, 3+2m, 3+4m, 3+6m) is an arithmetic progression, what is the common difference?

Correct answer: \(2m\)

Find the differences between consecutive terms: \((3+2m)-3=2m\), \((3+4m)-(3+2m)=2m\), and \((3+6m)-(3+4m)=2m\). Since every consecutive difference is the same, the common difference is \(2m\). \(m\) is not the increase between consecutive terms; subtract consecutive terms to obtain the difference. Exam tip: In an AP, verify using \(d=a_{n+1}-a_n\).