Consider the following decision table, How many cases are left when this decision table is collapsed? 2 credits [K3]

Question

Options

• A2
• B3
• C4
• D5

• A
  3% (2)
• B
  15% (10)
• C
  75% (51)
• D
  7% (5)

Explanation

Option C (4 cases) is correct because when a decision table is collapsed, rules with identical outcomes that differ in exactly one condition are merged using a "don't care" (–) value, reducing redundant combinations. Starting from the full set of condition combinations, the collapsing process eliminates only those rules that can be validly merged - leaving 4 irreducible cases that still cover all unique decision paths.

Why the distractors are wrong:

• A (2) over-collapses the table - merging too aggressively would lose coverage of distinct outcomes, making test coverage incomplete.
• B (3) under-collapses - one additional merge is still possible, so 3 is a valid intermediate step but not the fully collapsed result.
• D (5) leaves one redundant rule that can still be merged, meaning the collapse is incomplete.

Memory tip: Think of collapsing as "only merge rules if the action is identical and exactly one condition is free to vary." Count how many distinct outcome groups remain after all valid merges - that number is your collapsed case count. If your result is fewer cases than distinct outcomes or more than the original, you've gone too far or not far enough.

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