Question

Math

Posted 3 months ago

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The fraction $p$ of the population who has heard a breaking news story increases at a rate proportional to the fraction of the population who has not yet heard the news story.
Which equation describes this relationship?
Choose 1 answer:
(A) $\frac{d p}{d t}=k p$
(B) $\frac{d p}{d t}=k(1-p)$
(C) $\frac{d p}{d t}=1-k p$
(D) $\frac{d p}{d t}=-k p$
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Answer from Sia

Posted 3 months ago

Solution by Steps

step 2

The solution to this differential equation is $p(t) = c_1 e^{-kt} + 1$, where $c_1$ is a constant determined by initial conditions

step 3

This is a first-order linear ordinary differential equation, and the solution shows that the fraction $p$ approaches 1 as $t$ increases, which means eventually the whole population will have heard the news story

step 4

The term $kp(t)$ represents the rate of increase of $p$ due to the people who have heard the news, while $p'(t)$ is the actual rate of change of $p$

step 5

The correct form of the differential equation that describes the situation is $\frac{dp}{dt} = k(1 - p)$

B

Key Concept

Proportional rate of change

Explanation

The rate of change of the fraction of the population that has heard the news is proportional to the fraction that has not yet heard it, which is represented by the term $(1 - p)$.

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