Definition
Proportional reasoning
Proportional reasoning uses quantities that stay linked by the same multiplicative relationship.
What it means
Ask, “What factor changed this?” If 3 notebooks cost $12, doubling the number of notebooks doubles the cost. The pair 6 and 24 keeps the same relationship. Adding the same number to both quantities usually does not.
Remember it
Same relationship, same scale factor.
Example
Two fruit cups use 6 strawberries. At the same recipe rate, one cup uses 3 strawberries, so five cups use 5 × 3 = 15. The pairs 2:6 and 5:15 keep the same multiplicative relationship.
Watch for
A constant added amount is not enough. The pairs 2→5 and 4→7 both add 3, but they do not have the same ratio.
Common mix-up
Proportional does not simply mean that both numbers became larger; their multiplicative relationship must stay the same.
Exact meaning
Proportional reasoning is reasoning about quantities whose corresponding values are related multiplicatively, so equivalent pairs can be formed by scaling with the same factor and the ratio remains constant.