Inverse Variation

If I varies inversely with R and I = 0.15 when R = 50, which equation should be used to show this relationship?   A.I=7.5/R  B.I=7.5R  C.IR=0.75 D.I=R/7.5

If x varies inversely with y and x = 8 when y = 6, find y when x =10.
  A. y=40/3   B.y=5/12    C.y = 7.5  D.y = 4.8

xy = –12. What is the constant of variation for this relationship?
A.–1.2  B. -1/4    C.–0.12  D.–12

V varies inversely with T and V = 18 when T = 3. Which equation shows this relationship?  A.V=6/T  B.V=6T  C.V=54/T  D.V=54T

the 4 is in the doc.

[tex](1)\\R\cdot I=a\ \ \ \ and\ \ \ 50\cdot 0.15=a\\\\ \ \Rightarrow\ \ \ a=7.5\ \ \ \Rightarrow\ \ I= \frac{7.5}{R} \ \ \ \Rightarrow\ \ \ Ans.\ A.\\\\(2)\\x\cdot y=a\ \ \ and\ \ \ 8\cdot6=a\\\\ \ \Rightarrow\ \ \ a=48\ \Rightarrow\ \ \ xy=48\ \ \ \Rightarrow\ \ \ 10y=48\ \Rightarrow\ \ \ y=4.8\ \Rightarrow\ \ \ Ans.\ D.\\\\(3)\\xy=-12\ \ \Rightarrow\ \ \ constant=-12\ \ \Rightarrow\ \ \ Ans.\ D.\\\\[/tex]

[tex](4)\\xy=-12\\\\e.g.:\ \ \ x=3\ \ and\ \ y=-4\ \ \ \ or\ \ \ \ x=-3\ \ and\ \ y=4\ \ \Rightarrow\ \ Ans.\ A.\\\\(5)\\V\cdot T=a\ \ \ and\ \ \ 18\cdot 3=a\\\\ \ \ \Rightarrow\ \ \ a=54\ \ \ \Rightarrow\ \ \ V\cdot T=54\ \ \ \Rightarrow\ \ \ V= \frac{54}{T} \ \ \ \Rightarrow\ \ \ Ans.\ C.[/tex]