Question 810484
You can use the general point-slope formula
The given points are:
( 0, 1.8 ) and ( 4, 4 )
Time in years are plotted on the horizontal axis and
billions of sales are plotted on the vertical axis
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{{{ ( s - 4 ) / ( t - 4 ) = ( 1.8 - 4 ) / ( 0 - 4 ) }}}
This is ( change in y ) / ( change in x ) = ( change in y ) / ( change in x )
{{{ ( s - 4 ) / ( t - 4 ) = -2.2 / (-4) }}}
{{{  ( s - 4 ) / ( t - 4 ) = 1.1/2 }}}
{{{ 2*( s - 4 ) = 1.1*( t - 4 ) }}}
{{{ 2s - 8 = 1.1t - 4.4 }}}
{{{ 2s = 1.1t + 3.6 }}}
{{{ s = .55t + 1.8 }}}
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You are asked to find the point ( 16, s )
{{{ s = .55*16 + 1.8 }}}
{{{ s = 8.8 + 1.8 }}}
{{{ s = 10.6 }}}
There will be 10.6 billion in sales in 2016
check:
{{{  ( s - 4 ) / ( t - 4 ) = 1.1/2 }}}
{{{  ( 10.6 - 4 ) / ( 16 - 4 ) = 1.1/2 }}}
{{{ 6.6 / 12 = 1.1/2 }}}
{{{ 2*6.6 = 12*1.1 }}}
{{{ 13.2 = 13.2 }}}
OK
Here's the plot of the line:
{{{ graph( 400, 400, -2, 20, -2, 14, .55x + 1.8 ) }}}