All courses Algebra I · A-CED.2 2 of 76
Create equations in two or more variables, graph them, and label axes/scales appropriately.

Write a two-variable equation using a constant rate

Problem
Each ticket costs \(\$12\). Write an equation relating the number of tickets \(t\) to the total cost \(C\).
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Hint

Identify the constant rate, 12 dollars per ticket, and the variables t and C.

When there is no starting amount, the relationship is proportional: total = rate × number of items.

Solution walkthrough

01

Decode the variables

\[t~=~\text{number}~\text{of}~\text{tickets};~C~=~\text{total}~\text{cost}~\text{in}~\text{dollars}\]

The prompt assigns t to the ticket count and C to the resulting total cost. Thus t is the input and C is the output.

02

Identify the constant rate

\[\text{rate}~=~12~\text{dollars}/\text{ticket}\]

The phrase each ticket costs 12 dollars gives a rate of 12 dollars for every one ticket. There is no stated initial fee.

03

Use the proportional relationship

\[\text{total}~=~\text{rate}~\times~\text{count};~C~=~12t\]

A total with no starting amount equals the per-ticket rate multiplied by the number purchased. Substituting the stated rate gives C = 12t.

04

Check the units and a value

\[(12~\text{dollars}/\text{ticket})(2~\text{tickets})~=~24~\text{dollars};~C~=~12(2)~=~24\]

Ticket units cancel and leave dollars, as C requires. Two tickets would cost 24 dollars, confirming that the total grows by 12 dollars per ticket.

05

State the equation

\[C~=~12t\]

The equation relates the requested ticket count to total cost and exactly matches choice A.

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Another way

  1. View the cost as repeated addition: t copies of 12 dollars sum to 12t dollars.

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Common mistake

Do not write C = 12 + t. Twelve is a dollars-per-ticket rate, so it multiplies the number of tickets; it is not a fixed starting charge.

Solution walkthrough video