Trade Math · Fractions
Adding, subtracting, multiplying & dividing fractions
Fractions are the currency of trade math. Tape-measure readings, pipe dimensions, material orders — all fractions. Here's how to add, subtract, multiply, and divide them cleanly on paper, without a calculator, the way UA aptitude tests commonly assess.
Cheat sheet
- Add or subtract: get a common denominator, then add or subtract the numerators. Denominator stays the same.
- Multiply: numerator × numerator, denominator × denominator. Then reduce.
- Divide: invert the second fraction and multiply. ("Keep, change, flip.")
- Mixed numbers: convert to improper fractions before operating, then convert back at the end.
- Always reduce to lowest terms as the last step.
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