David W. answered • 10/12/15
Tutor
4.7
(90)
Experienced Prof
To convert the units of a value, we use the multiplicative identity (that is, 1) because we may multiply any number by 1 without changing its value, only its units.
In this case we need the value 1 = (1 dozen / 12).
Note: When we multiply: (cost / dozen) * (dozen), dozen cancels out, leaving only cost.
total cost = (cost per dozen) * ( number of dozens)
total cost = (cost per dozen) * ( (24) * (1 dozen /12) ) [convert units]
total cost = ($10.75 / dozen) * ( (24) * (1 dozen /12) ) [insert cost]
total cost = ($10.75) * ( (24) /12 ) [now it is only $]
(note: teachers and tutors have done the above steps thousands of times and they forget that students are just learning them -- they even forget multiplicative identity. another note -- there is also an additive identity; what is it?)
total cost = ($10.75) * (2)
total cost = $21.50
