Definition
Unitary method
The unitary method finds one unit first, then scales to the number of units needed.
Continue from this idea into connected AXIO math.
Boundary check: This works only for direct proportion; a fixed fee would break the method.
What it means
Go to one, then go to the amount you need. If 4 books cost $20, divide by 4 to find that one book costs $5. Then multiply by 7, so seven books cost $35. This works when equal units have equal value.
Remember it
Many → one → needed many.
Example
Six identical juice boxes hold 1.8 litres altogether. One box holds 1.8 ÷ 6 = 0.3 litres. Nine boxes hold 9 × 0.3 = 2.7 litres.
Watch for
Do not use the method as a direct-proportion shortcut when the relationship has a fixed extra charge, such as a taxi fare with a starting fee.
Common mix-up
Finding one unit is the middle step; the problem may still ask for a different number of units.
Exact meaning
The unitary method solves a proportional problem by first finding the value of one unit, then multiplying or dividing to find the value for the required number of equal units.