# FAQs For Lab 3

(Return to Online Intro)

**Calculations**

- How can I determine
when the fish population reaches 9,000?

Simply look at your table. Your table gives you an estimate for the fish
population in each month; use these estimates to find where the population
first dips below 9,000.

Recall, each reading is taken on the first of the month.

- How
can I show a formula is a solution to an initial value problem?

You need to show both that it satisfies the differential equation, and
that it satisfies the initial condition. To show that a function is a
solution to a differential equation, you need to plug in the formula for
*Q* (including plugging in the derivative for *Q*') and
show that the equation is true. (See the example in your text on p. 49,
in section 10.2 for a demonstration of how this works.)

To see that the initial condition is satisfied, just plug in *t* = 0
and make sure that your equation does in fact give you *Q = *9,500
as desired.