Elimination or Substitution? How to Choose the Faster Method
There is no need to force one method every time. A quick look at the coefficients usually tells you which route will be shorter.
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Maths notebook
Short explanations for the bits that usually cause mistakes
These posts focus on one question at a time: why a method works, where people commonly go wrong, and how to check the result.
Surface Area of a Cuboid Without Missing a Face
A cuboid has three pairs of matching faces, so surface area is the sum of all three pair areas.
Read the explanation →The Ratio Rule That Prevents Most Unit Mistakes
Before simplifying a ratio, make sure both quantities use the same unit. That one habit prevents a large class of mistakes.
Read the explanation →Portable Power Bank Buying Guide: Capacity, USB-C and Airline Limits
How to understand watt-hours, usable capacity, USB-C Power Delivery and travel considerations when choosing a power bank.
Read the explanation →Monitor Arm Buying Guide: Desk Compatibility, Weight and Range
How to compare monitor arms by VESA support, desk mounting, monitor weight and useful movement range.
Read the explanation →Cordless Vacuum Buying Guide: Runtime, Floor Heads and Maintenance
How to compare cordless vacuums by realistic runtime, floor tools, bin design, batteries and ongoing maintenance.
Read the explanation →Percentage Points vs Percentage Change: The Difference in One Example
If a rate rises from 20% to 25%, the increase is 5 percentage points but 25% in relative terms. Those are different statements.
Read the explanation →Adjustable Dumbbells Buying Guide for Small Home Gyms
How to compare adjustable dumbbells by weight range, change mechanism, handle size, storage and floor space.
Read the explanation →Angles on Parallel Lines: Which Pair Are You Looking At?
Naming the angle pair first often prevents using the wrong rule on parallel-line diagrams.
Read the explanation →Why 15% Off and 15% Back Does Not Return to the Starting Price
A percentage decrease and the same percentage increase act on different starting amounts. Here is the quickest way to see the difference.
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