How do you write each real-world example as a rate using labels and then the unit rate: Maddy put 72 chairs in 4 rows?

As a rate: for every 4 rows you have 72 chairs.

This is a word version of ratio which can be written in 2 ways

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In the form you sometimes see on electronic clocks, which is not a convenient format for calculations

#" "72:4#
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In the same form as you use for fractions which is much better for manipulating changing quantities.

#" "72/4" or "4/74" depending on needs"#
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#color(blue)("Determining unit rate")#

I chose to make the unit rate to be based on 1 row.

#color(brown)("Labeled ratio in initial rate")#

#" "("Chair count")/("Row count") -> 72/4#

#color(brown)("Labeled ratio in unit rate")#

#" "("Chair count")/("Row count") -> 72/4 -=(72-:4)/(4-:4) = 18/1#

#color(blue)("So the unit rate is 18 chairs per row")#