Mental Math Shortcuts Every Student Should Know Before Exams

Picture this: you're taking an exam, time’s ticking, and you’re stuck on a simple calculation.

Sound familiar?

Exams aren't just about knowing the what — they're about handling the how fast. And that’s where mental math shortcuts come in.

By mastering a few clever techniques, you can save precious time, boost your confidence, and avoid silly mistakes.

Let’s break down the mental math moves every student should have in their toolkit — before walking into any test hall.

1. Multiply by 5, 25, or 50 in Seconds

× 5

Divide by 2 and add a zero.
Example: 48 × 5 = (48 ÷ 2) → 24 → add 0 → 240

× 25

Divide by 4 and add two zeros.
Example: 64 × 25 = (64 ÷ 4) = 16 → 1600

× 50

Divide by 2 and add two zeros.
Example: 38 × 50 = (38 ÷ 2) = 19 → 1900

2. Square Numbers Near a Base (like 100)

This trick is gold for fast squaring.

Example: 103²

• Base = 100 → difference = 3
• Step 1: 103 + 3 = 106
• Step 2: 3² = 9
• Final answer: 10609

(Just add the number and its difference, then tack on the square of the difference.)

3. Find Percentages Fast

Forget the long method. Just break it into chunks.

Example: 18% of 250

• 10% of 250 = 25
• 5% = 12.5
• 3% = 7.5
• Add: 25 + 12.5 + 7.5 = 45

Done in under 15 seconds — all in your head.

4. Multiplying Two-Digit Numbers with a Common First Digit

Example: 63 × 67

• Both start with 6 and differ by 4
• Step 1: Square the common digit → 6² = 36
• Step 2: Add the last digits: 3 × 7 = 21
• Step 3: Add common digit × (next digit) → 6 × 7 = 42
• Answer: 4221

Or simply apply:
(x + y)(x - y) = x² - y²
This works wonders for numbers like 102 × 98

5. Division by 5

Multiply by 2 and move the decimal.

Example: 86 ÷ 5
→ 86 × 2 = 172
→ Move decimal one place left = 17.2

6. Doubling and Halving

This works especially well for multiplying uneven numbers.

Example: 25 × 16
→ Halve one, double the other: 12.5 × 32
→ Not helpful.

But try:
25 × 16 = (50 × 8) = 400

Pick the right pair to make the numbers simpler!

7. Subtracting from 1000, 10,000, etc.

This is especially useful in aptitude tests.

Example: 1000 – 367
Subtract each digit from 9, and last from 10:
→ 9 – 3 = 6
→ 9 – 6 = 3
→ 10 – 7 = 3
Answer: 633

Why These Tricks Matter

Exams aren't just about knowing. They're about doing, and doing it under pressure.

With these shortcuts:

• You’ll skip over slow, error-prone methods
• You’ll finish with time to review
• You’ll build confidence going into math-heavy sections

And the best part? These are habits you can build in just 5 minutes a day.

Practice Idea: Make It a Game

• Take 10 random questions before bed
• Time yourself: can you do them under 3 minutes?
• Try beating your best time every day

It’s not about speed for the sake of speed. It’s about freeing your brain to focus on the tougher thinking — the actual problem-solving.

Final Thought: Make Math Work For You

Mental math isn't a fancy trick for show-offs. It’s a practical skill that any student can learn.

Start with one or two shortcuts. Build the muscle. And when exam day comes, you won’t just be faster — you’ll be calmer, too.

Because you trained your brain to think like a pro.