Question

Marne Shia walked 3/8 of a mile in 3/5 of an hour. What equation can be used to calculate her unit rate in miles per hour?

Answer 1

three eighths over three fifths = five eighths mile per hour

Explanation:

Answer 2

speed = (3/8 mi)/(3/5 h)

Explanation:

... speed = distance/time

Fill in the given values:

... speed = (3/8 mi)/(3/5 h)

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Comment on units

You can use the units to provide both guidance and assurance. You know speed is generally expressed in miles per hour. If you consider "per" to mean "divided by", this expression of units tells you speed is calculated by dividing miles by hours.

If you leave the units with the numbers, as we have above, they enter into the calculation the same way any variable might. You can do the arithemetic with the numbers, and you can indicate the arithmetic with the units (just as you would with any variables). Here, the result of evaluating the equation would be ...

`\displaystyle\frac{(3)/(8)\,\text{mi}}{(3)/(5)\,\text{h}}=((3)/(8))/((3)/(5))\,\frac{\text{mi}}{\text{h}}=(5)/(8)\,\text{mi/h}`

The fact that the units come out mi/h (the units of speed) provides assurance that you probably did the math correctly.