SIG Probability Interview 2027: Torpedo Boat Question Explained

The answer is 5/9, or about 55.6%. Use the complement: the boat survives only if both torpedoes miss, — P(both miss) = (2/3)² = 4/9, so P(destroyed) = 1 − 4/9 = 5/9. This "sig torpedo probability question" is commonly reported by candidates as a test of whether you reach for complements instead of enumerating cases.

SIG Torpedo Probability Question: What This Question Assesses

The question checks two things: that you recognize "destroyed" means "at least one hit," and that you compute "at least one" via the complement rather than adding P(first hits) + P(second hits) and double-counting the both-hit case. It is a speed test — SIG interviewers expect the complement move to be reflexive.

SIG Torpedo Probability Question: How to Answer

• Reframe as "at least one hit." The boat is destroyed unless every torpedo misses.
• Compute the survival probability. Each torpedo misses with probability 1 − 1/3 = 2/3. Two independent misses: (2/3)² = 4/9.
• Take the complement. P(destroyed) = 1 − 4/9 = 5/9 ≈ 55.6%.
• Verify against the alternative method. Adding cases: P(first hits) + P(first misses, second hits) = 1/3 + (2/3)(1/3) = 1/3 + 2/9 = 5/9. Same answer — mention this only if asked to double-check.

Sample line: "The boat survives only if both torpedoes miss, which is (2/3) squared, or 4/9 — so the destruction probability is 5/9, about 56%."

Common Mistakes

• Adding 1/3 + 1/3 = 2/3, double-counting the case where both torpedoes hit.
• Computing 1/3 × 1/3 = 1/9 and calling it the answer — that is the probability both hit, not at least one.
• Assuming dependence between the shots when the question gives independent hit probabilities.

Missing the complement trick here signals to the interviewer that harder conditional-probability questions will be rough. Drill "at least one" problems until the complement is your first move. Formats may vary by role and region; confirm details on SIG's official careers page.

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FAQ

What is the probability the boat is destroyed with two torpedoes at 1/3 hit chance each? 5/9, about 55.6% — one minus the probability that both miss, (2/3)² = 4/9.

Why use the complement instead of adding probabilities? Adding P(first hits) + P(second hits) double-counts the both-hit scenario. The complement handles "at least one" cleanly.

Is the torpedo question a real SIG interview question? Torpedo-style probability questions are commonly reported by candidates in SIG interviews, though exact wordings may vary by role and region.

What is the general rule for "at least one" probability questions? Compute 1 minus the probability that the event never happens — it is almost always faster than enumerating every success case.

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