6. At the beginning of school, Julie bought one 3-subject notebook and four single-subject notebooks for $1$. If the 3-subject notebook cost twice as much as a single-subject notebook, how much did each Type of notebook cost?

3-subject notebook cost $0.67 or 67 cents and the single-notebook cost  $0.33 or 33 cents.

Step-by-step explanation:

Let's represent the 3-subject notebook by y and the single-notebook by x.

y has to cost twice as much as x and we can represent that by the equation

y = 2x  

We now know that the total cost of the 3-subject notebook and the single-subject notebook has to equal  $1.

We can also represent that by the equation and solve for x

2x + x = 1  

3x = 1

x = 0.33   $0.33 or 33 cents  

If the single-subject is $33 cents then subtract it from a dollar to see how much the 3-subject notebook costed.

1- 0.33 = 0.67

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