Because Z is directly proportional to X and inversely proportional to Y, therefore
[tex]Z=k( \frac{X}{Y}),\\k=constant [/tex]
When X=10 and Y=4, Z=47.5.
Therefore
k(10/4) = 47.5
2.5k = 47.5
k = 19.
That is,
[tex]Z= \frac{19X}{Y} [/tex]
When X=13 and Y=10, obtain
Z = (19*13)/10 = 24.7
Answer: 24.7
