Read the pattern of letters, numbers/terms, and find the missing term from the…

Concept

An invariant is a quantity that remains unchanged across all terms generated by a rule.

For a three-digit number with digits a, b, and c, a candidate rule may combine those digits; a missing term must preserve the same invariant value as every given term.

Application

1. Let a be the hundreds digit, b the tens digit, and c the units digit. Test the rule a × b + c.

2. For 266, 2 × 6 + 6 = 18.

3. For 339, 3 × 3 + 9 = 18.

4. For 528, 5 × 2 + 8 = 18. Thus the invariant value is 18.

Cross-check

Apply the same rule independently to every offered value:

Only 630 gives the invariant value 18, so the missing term is 630.