The number of cell phones in the united states was 1.2 million in 1995. if the annual increase in the number of phone per year is 21%. in what year will there be 1 billion cell phones in use

Year 2031

Step-by-step explanation:

We need to use the formula for compound growth here, that is:

Where

F is future amount (1 billion)

P is present amount (1.2 million)

r is rate of growth (21% or 0.21)

t is the time (we need to find this)

Putting in the values we have:

So after about 35.28 years, the number of phones will cross 1 billion, so we take the next year, so after 36 years.

From 1995 to 36 years would be the year 2031

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