A newspaper has a circulation of 900000 readers An ad that r

A newspaper has a circulation of 900,000 readers. An ad that runs for x days will be seen by A(x)=900,000-(450,000/x) people. How fast is the number of potential customers growing when the ad has run for 7 days? (Round to the nearest whole number and give appropriate units)

Solution

A(x)=900,000-(450,000/x) ( no. of people seeing the ad) ;  x days

How fast is the number of potential customers growing ?

Find rate of people seeing the ad with every passing day

dA/dx = 450,000/x^2

when x=7 ; dA/dx = 450,000/49 = 9183.67

= 9184 persons/ day