Answer :
Suppose 6 people can plant 12 trees in 3 hours. So, The people are needed to plant 28 trees in 5 hours and 15 minutes is 8.
What is the unitary method?
The unitary method is a method for solving a problem by the first value of a single unit and then finding the value by multiplying the single value.
The time, t, in hours, that it takes x people to plant n trees varies directly
with the number of trees, and inversely with the number of people.
[tex]t \propto n\\\\t \propto \dfrac{1}{x}[/tex]
Suppose 6 people can plant 12 trees in 3 hours.
[tex]3 = 6k\\\\k = 1/2\\\\[/tex]
So, the people are needed to plant 28 trees in 5 hours and 15 minutes
= 8
Learn more about the unitary method;
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