Count on to the next whole hour, then the hours, then the leftover minutes. Works every time.
Start time · End time
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The metric staircase. Every step is ten, so converting is just sliding the decimal point.
Inches, feet, pounds, cups. No pattern to lean on — so go down to the smallest unit and back up.
The two get mixed up constantly. One is the walk around the edge, the other is the space inside.
An L-shape is just two rectangles. Slice it, do each piece, add them up.