Now, to make things concrete, we will assign values $a=0\mathrm{.}000002$ and $b=0\mathrm{.}04($in the units your found$)$ to these coefficients.

Question $2.$ On average, how long does a person who buys the product remain an active user? Explain.

Plugging our values of a and $b$ into the SIR equations, we have

$S^{\text{'}},=-0\mathrm{.}000002SI,$

$I^{\text{'}},=0\mathrm{.}000002SI-0\mathrm{.}04$I,

$R^{\text{'}},=,0\mathrm{.}04$I.

To predict how things evolve, we need to say how they start. So let's assume that we start with $100,000$ potential users, $5,000$ active users, and no people who have rejected the product. Question $3.$ How large is the overall population that we're working with? Explain.