Four groups of three numbers are given. In each group, the second and third numbers follow an addition rule from the first. Three groups share the same rule; select the odd group.

Introduction / Context:
This is another number pattern question where each group of three numbers follows a simple addition rule from the first term. Your goal is to identify the group that does not fit the rule followed by the majority.

Given Data / Assumptions:

• Groups: (9, 11, 14), (13, 15, 18), (17, 19, 22), (21, 23, 28).
• Second and third numbers are derived from the first number.
• We look for a pattern like first + constant1 and first + constant2.

Concept / Approach:
A quick way is to subtract the first number from the second and third numbers in each group and check if the pair of differences is the same for three groups. That repeated pair reveals the rule; the group with a different pair of differences is the odd one out.

Step-by-Step Solution:
(9, 11, 14): 11 - 9 = 2 and 14 - 9 = 5. (13, 15, 18): 15 - 13 = 2 and 18 - 13 = 5. (17, 19, 22): 19 - 17 = 2 and 22 - 17 = 5. (21, 23, 28): 23 - 21 = 2 but 28 - 21 = 7, not 5. Thus in the first three groups the second and third terms are first + 2 and first + 5, whereas the last group uses first + 2 and first + 7.

Verification / Alternative check:
You can also directly express the second and third terms as formulas: for the first three groups, second = first + 2 and third = first + 5. When you apply the same rule to 21, you would expect 21, 23, 26, but the actual group is 21, 23, 28. Since 28 does not equal 21 + 5, the pattern breaks here, confirming that the fourth group is different.

Why Other Options Are Wrong:

• (9, 11, 14): Follows the rule first + 2 and first + 5.
• (13, 15, 18): Also follows exactly the same addition rule.
• (17, 19, 22): Matches the same pattern of +2 and +5 from the first term.

Common Pitfalls:
Some candidates may look only at whether the numbers are increasing and ignore the exact size of the jumps. All groups increase, but the size of the second jump is crucial. Ignoring the precise difference can easily make the last group seem normal when it actually breaks the rule followed by the others.

Final Answer:
(21, 23, 28)