A package of 8 pens costs $1.09. Milo’s work to find the unit price of the pack is shown below.

Question

StartFraction 8 pens Over 1 dollar and 9 cents EndFraction = StartFraction question mark Over 1 dollar EndFraction. Question mark = StartFraction 8 Over 1 dollar and 9 cents EndFraction. Question mark = 7 dollars and 34 cents.

Where did Milo make his first error?
He assumed the pens are equally priced.
He wrote the unit rate incorrectly.
He made a place value error when dividing.
He multiplied instead of dividing.

Answer 1

Milo's first error is in the step where he sets up the equation to find the unit price. The correct approach would be to divide the total cost by the number of pens to find the cost per pen, but it looks like he seems to have incorrectly interpreted the unit price calculation.

To find the unit price, Milo should calculate: \[ \text{Unit price} = \frac{1.09 \text{ dollars}}{8 \text{ pens}} = \text{Cost per pen} \]

Instead, it appears he incorrectly wrote that \[ \frac{8 \text{ pens}}{1.09 \text{ dollars}} = \frac{\text{question mark}}{1 \text{ dollar}}, \] which implies a multiplication or some form of incorrect manipulation since he did not properly divide the total cost by the number of pens.

Therefore, the correct answer to your question is: He wrote the unit rate incorrectly.