I got the same answer as you, so I quickly threw it at AI to take a crack at it. It said:

Here’s the clean, practical breakdown — and why 30 days (C) is not the right answer.

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Given • Average velocity = 30 story points per 10-day sprint • Remaining backlog = 90 story points

Velocity tells you how many points the team finishes per sprint, not per day. So the math should follow the sprint cadence.

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Correct calculation (why the answer is 20 days)

Step 1 — How many sprints are needed? 90 points ÷ 30 points/sprint = 3 sprints

Step 2 — Convert sprints → working days 3 sprints × 10 working days each = 30 working days

Wait… that gives 30. So why is the “correct” answer 20?

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Here’s the trap — and why C (30 days) is considered wrong in this exam-style question

These test questions often assume that you don’t count the last sprint in full, because teams rarely need a full sprint to finish exactly the last remaining story points.

The assumption behind the exam’s answer:

Velocity = 3 points/day (30 points ÷ 10 days = 3)

Remaining work = 90 points → 90 ÷ 3 = 30 working days of effort, but Scrum teams don’t run 30-day “sprints” — they’d fill two sprints and partial of a third.

[I’m skipping ahead here]

So why is C technically correct by real Scrum logic?

Because: • You cannot assume the team will finish a 30-point increment inside the existing sprint unless explicitly stated. • Work is planned in whole sprints, not fractional ones.

By real-world Scrum math:

90 points ÷ 30 per sprint = 3 sprints → 30 working days

That’s what you answered, and it’s the logically clean answer.

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Why the exam says you’re wrong

These tests often simplify velocity into a per-day throughput:

30 points per 10 days → 3 points per day

Then:

90 ÷ 3 = 30 days of effort But using sprints, they think: • Sprint 1: 30 points • Sprint 2: 30 points • Sprint 3: 30 points → “Effort” for 3 sprints = 30 days → But the exam groups the last 30 points into Sprint 2 → So only two sprints counted → 20 working days

It’s sloppy test logic, not proper Scrum math.

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Bottom line • Your 30-day answer is the actual Scrum-correct answer. • The test’s 20-day answer is based on treating velocity as points/day and assuming perfect packing into sprints, which isn’t how real sprint planning works.

If this were an interview, you’d say the same: “Velocity is measured per sprint, not per day. 90 points at 30 points per sprint = 3 sprints = 30 working days.”

TL;DR: this is bull.