ANSWER
C. 35 men
EXPLANATION
Let m represent the number of men needed and d represent the number of days.
From the question,the number of men needed varies inversely to the time needed to complete the project.
We can write the inverse variation equation.
[tex]m = \frac{k}{d} [/tex]
where k is the constant of variation.
When m=28, d =90.
We substitute these values into the variation equation to determine the value of k.
[tex]28 = \frac{k}{90} [/tex]
[tex]k = 90 \times 28[/tex]
[tex]k = 252[/tex]
Now the equation becomes:
[tex]m= \frac{2520}{d} [/tex]
When d=72,
[tex]m = \frac{2520}{72} [/tex]
[tex]m = 35[/tex]
Therefore he needs to have 35 men working.
