السؤال 116

A water bill is $12 each month plus$ 3 for every cubic metre used. Which proportionality judgment is correct?

It is directly proportional because the bill always increases.
It is inversely proportional because greater use raises the bill.
It is not directly proportional because zero use still costs $12.الإجابة الصحيحة
It is directly proportional because each cubic metre adds $3.

الشرح

The bill is $12 even when no water is used, so it does not pass through the origin and is not directly proportional to usage. The fixed$ 3 variable rate may suggest proportion, but the unchanged monthly charge makes the bill-to-usage ratio vary.

الشرح

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