4 Mental Maths Strategies Every OC Candidate Should Know
The mathematical reasoning section gives your child 35 questions in 40 minutes. That’s just over a minute per question. The children who finish comfortably aren’t necessarily better at maths. They’ve learned strategies that help them work faster and smarter.
Here are four that every OC candidate should have in their toolkit.
1. Friendly numbers
Rounding one number to make a calculation easier, then adjusting.
Your child sees 47 x 6. That’s messy. But 50 x 6 is easy: 300. Then subtract the 3 x 6 you added: 300 - 18 = 282. Two simple steps instead of one hard one.
This works any time a number is close to a round number, and it turns messy arithmetic into something your child can do in their head.
2. Working backwards
Starting from the answer choices and testing which one works, instead of solving from scratch.
“What number, when multiplied by 8 and then reduced by 12, gives 60?” Instead of setting up an equation, plug in an answer choice: try 9 → 9 x 8 = 72, 72 - 12 = 60. Done.
The test is multiple choice. The correct answer is always right in front of your child. Working backwards takes advantage of that.
3. Process of elimination
Systematically ruling out answers that can’t be right before solving.
A question says a shop buys something for $45 and sells it for $72, then asks for the profit. The options are $17, $27, $72, $95, and $117. The word “profit” means revenue minus cost, so it must be less than the $72 revenue. That eliminates $72 and $117 immediately. Your child has narrowed five options down to three before doing any arithmetic.
Even ruling out one option improves the odds significantly when time is tight. This should be the first step on every question.
4. Number properties
A specialised form of process of elimination that uses rules about odd/even numbers, last digits, and divisibility to rule out answers instantly.
A question asks for the product of two even numbers. The options are 136, 217, 348, and 455. The product of two even numbers must be even, so 217 and 455 are gone immediately. No calculation needed.
Children who understand number properties can often eliminate half the options in seconds. That’s an edge that pure calculation speed can’t match.
These strategies are learnable
None of this is innate talent. These are skills that can be taught, practised, and mastered. The key is deliberate practice: not just hearing about the strategy, but working through examples until it becomes automatic under test pressure.
On OC Test Prep, our Strategy Library teaches each of these strategies step-by-step with video tutorials and interactive exercises. Your child doesn’t just learn what the strategy is. They practise it until it clicks.