Question

A newspaper is launching a new advertising campaign in order to increase the number of daily subscribers. The newspaper currently ​(t​0) has​ 26,000 daily subscribers and management expects that​ number, S(t), to grow at the rate of subscribers per​ day, where t is the number of days since the campaign began. How long​ (to the nearest​ day) should the campaign last if the newspaper wants the number of daily subscribers to grow to​ 49,000?

Answer 1

57 days

Explanation:

Given that:

t(0) = 26000

Growth rate (S'(t)) = 80t^1/2

Targeted number of subscribers = 49000

Take the integral of the growth rate :

∫80t^1/2dt = [(80t^(1/2 + 1)) / 1/2 + 1] + C

[(80t^(1/2 + 1)) / 1/2 + 1] + C = (80t^3/2) / 3/2 + C

(80t^3/2) * 3/2 + C = (160/3)t^3/2 + C

(160/3)t^3/2 + C

Let C = t(0)

(160/3)t^3/2 + 26000 = 49000

(160/3)t^3/2 = 49000 - 26000

(160/3)t^3/2 = 23000

Multiply both sides by 3/160

t^3/2 = 23000* 3/160

t^3/2 = 69000/160

t^3/2 = 431.25

t^(3/2 * 2/3) = 431.25^2/3

t = 57.080277

t = 57 days (approx.)