The number N of US cellular phone subscribers (in millions) is shown in the tabl

Question

The number N of US cellular phone subscribers (in millions) is shown in the table. (Midyear estimates are given.)

(a) Find the average rate of cell phone growth between the following years. In each case, include the units. (Round your answers to one decimal place.)

(i) from 1998 to 2002
____________________ million phones/yr

(ii) from 2000 to 2002
____________________million phones/yr

(iii) from 1998 to 2000
____________________million phone/yr

(b) Estimate the instantaneous rate of growth in 2000 by taking the average of the two average rates of change in (ii) and (iii).

What are its units?
_____________________million phones/yr

Explanation / Answer

a) i) (141-69)/(2002-1998) = 72/4 = 18 million phones/yr

ii) (141-109)/(2002-2000) = 32/2 = 16 million phones/yr

iii) (109-69)/(2000-1998) = 40/2 = 20 million phones/yr

b) (16+20)/2 = 36/2 = 18 million phones/yr

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