Sum of ages of Raj and Ravi is 8 years more than the sum of ages of Ravi and Rahul.

Since the common person (Ravi) appears on both sides of the equation, cancel his age directly. The difference between the remaining individuals (Raj and Rahul) must equal the given surplus of 8 years.

Students often try to assign arbitrary ages to Ravi (e.g., setting Ravi's age to 20), which is unnecessary and time-consuming; the variable $R_v$ is irrelevant as it cancels out.

This logic is identical to balance-scale problems in Physics or accounting reconciliation, where common terms on both sides of an equality cancel out.