Step-by-step Solution:

Quick Solution

This puzzle requires us to first translate the symbolic expression into plain English using the provided definitions, and then deduce the age ranking of the three individuals.

1. Understand the Symbol Meanings

Let's list the rules for the operators:

• A * B means A and B are the same age (A = B).
• A - B means B is younger than A (A > B).
• A + B means A is younger than B (A < B).

2. Decode the Expression: Sachin * Mohan - Ravi

We can break the expression down into two logical parts:

1. Sachin * Mohan: Applying the `*` rule, this translates to:
   Sachin's age = Mohan's age.
2. (Sachin * Mohan) - Ravi: This is in the form of `A - B`, where `A` represents the `(Sachin * Mohan)` group. Since they are the same age, we can treat this as `Mohan - Ravi`. Applying the `-` rule, this translates to:
   Ravi is younger than Mohan (or Mohan > Ravi).

3. Determine the Final Ranking

By combining our two deductions, we get the complete age order for the three people:

Sachin = Mohan > Ravi

This ranking clearly shows that Sachin and Mohan are the oldest (and the same age), and Ravi is younger than both of them.

Final Answer: The statement that must be true is that Ravi is youngest.