1. Fairy Straightforward Proportionality Problem

Hey Guys,

This one doesn't involve any real math all too much, but I'm still getting confused on it, help? Thanks!

The rate R that a certain disease spreads is proportional to the number of infected individuals and is also proportional to the number of uninfected individuals. The total population is P and the number of infected individuals is D. Express the rate that the disease spreads in terms of this information. Use C as your proportionality constant.
R(P,D)=_______________

(EDIT: I can't believe I misspelled "fairly" in the title, sorry!)

2. Hello Togechu64
Originally Posted by Togechu64
Hey Guys,

This one doesn't involve any real math all too much, but I'm still getting confused on it, help? Thanks!

The rate R that a certain disease spreads is proportional to the number of infected individuals and is also proportional to the number of uninfected individuals. The total population is P and the number of infected individuals is D. Express the rate that the disease spreads in terms of this information. Use C as your proportionality constant.
R(P,D)=_______________

(EDIT: I can't believe I misspelled "fairly" in the title, sorry!)
If there are $D$ individuals infected, and $P$ in total, then there are $(P-D)$ uninfected. So $R$ is proportional to $P$ and to $(P-D)$; i.e. $R = CD(P-D)$.