I Never Thought to Test This — Until a Meme Exposed My QA Blind Spot

It started with a meme. One of those “stupid math puzzles” meant to bait arguments online:

130 + 100 × 5 = 630
100 + 130 × 5 = 750
230 × 5 = 1150

At first, I laughed. Then I ran it on my Windows calculator, switching to scientific mode to confirm. Everything checked out—until it didn’t. The calculations were correct, but the way they were grouped made me realize something that hit harder than expected:

I’ve never once tested logic grouping or operator precedence in QA.

Not in my test cases. Not in user flows. Not even in prompt logic when using AI. I assumed the logic was a dev’s job—and that it would “just work.”

That’s the kind of assumption that lets quiet logic bugs slip through.

What Is Operator Precedence and Logic Grouping? (And Why You Should Care)

🔹 Operator precedence is the order in which operations are performed. Math engines and most programming languages calculate multiplication and division before addition or subtraction.

Example:

100 + 130 × 5 = 750

Because it becomes:

130 × 5 = 650 → 100 + 650 = 750

🔹 Logic grouping is when you use parentheses to override that default order.

(100 + 130) × 5 = 1150

You’re telling the calculator or program: do this group first.

If you’ve never tested for these in your QA suite, you’re not alone. I hadn’t either—until this meme knocked it into focus.

The Meme Breakdown and My Own Tests

This was the original meme:

130 + 100 × 5 = 630
100 + 130 × 5 = 750
230 × 5 = 1150

Out of curiosity—not obligation—I started testing all the variants to see what broke. I’m a QA lead, not the main tester, but I stay sharp by checking edge cases like these. Here’s the full test set I tried:

130 + 100 × 5 = 630
100 + 130 × 5 = 750
230 × 5 = 1150

100 × 5 + 130 = 630
130 × 5 + 100 = 750
230 × 5 = 1150

(130 × 5) + 100 = 750
(100 × 5) + 130 = 630
(130 + 100) × 5 = 1150
(100 + 130) × 5 = 1150

Every line returned the correct result—because PEMDAS kicked in. The engine respects operator precedence, even if the input order changes. This isn’t just a math issue. It’s a logic awareness gap in how we test.

What Most QA Teams Overlook

Logic grouping and operator precedence are typically treated as developer-level logic. Most manual testers don’t dive that deep—unless you’re an SDET or you’re testing financial formulas directly.

Until now, I hadn’t flagged this as a test case area. I focused on output validation, not internal calculation flow.

But as a QA lead, I recognize that even if I don’t test this hands-on, I need to raise it as a risk factor. This isn’t about rewriting how we work—but refining when and where we zoom in.

👉 Related: The Test Methodologies You Need to Know to Be Dangerous

Where the Logic Bug Hides in Code

Say you’re testing a pricing rule and the dev (or AI assistant) writes:

let total = base + discount * tax;

It returns a number. No error. But it’s wrong.

The logic actually needs to be:

let total = (base + discount) * tax;

That’s the difference between correct math and silent underbilling—or overcharging.

Your job isn’t to rewrite the formula. It’s to question it hard enough that the dev:

• Confirms logic was grouped correctly
• Or realizes it wasn’t, and fixes it before production

👉 Related: AI-Assisted Manual Testing: The Hidden Power Combo Most QA Teams Ignore

Why This Quietly Breaks Real Systems

Logic grouping bugs don’t crash software. They distort results:

• In billing: customers get undercharged—or worse, overcharged.
• In rewards: users earn less than they should.
• In metrics: you report false numbers.

Here’s the breakdown:

let base = 1000;
let discount = 200;
let tax = 1.12;

// AI or rushed dev version:
let total = base + discount * tax;     // 1000 + (200 * 1.12) = 1224

// Correct logic:
let total = (base + discount) * tax;   // (1000 + 200) * 1.12 = 1344

A ₱120 difference per transaction. At 10,000 customers? That’s ₱1.2M lost—or accidentally stolen.

👉 Related: The Lost Art of Debugging in QA

How I’ll QA Logic Chains Moving Forward

This isn’t something I test professionally today. But as the QA lead, I’m flagging it so our team can build awareness before it becomes a real issue. Here’s how we’ll approach it when it applies:

1. Explicitly test math logic — not just the output.
2. Add grouped and ungrouped cases to expose PEMDAS flaws.
3. Reverse-calculate results — independently.
4. Highlight vague logic in stories or Jira tasks.
5. Ask for subtotals and logs — during debugging.
6. Request a verbal formula breakdown — a quick sanity check.

👉 Related: I’m Not an Automation Engineer — But Here’s How I Use Playwright to Boost QA Anyway

Final Thought: When a Meme Becomes QA Training

I’ve never run into this in a live production app yet. But I know now: if we ever do fintech, billing, or payout logic, this gets raised.

And it all started with a meme.

The thing is—most QAs don’t think to test for this. We trust the formula. We assume the math engine just works. And it usually does. But if the logic’s wrong, so is the result.

This is how you lose money—or worse, lose trust. That’s why logic grouping isn’t just a dev thing anymore. It’s a QA checkpoint, too.

Jaren Cudilla
Not once tested operator precedence. Now it’s on the checklist.

Runs QAJourney.net to expose the quiet bugs—like logic grouping errors that never crash, but always corrupt. Writes for testers who don’t just check boxes—they question the formula.

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