Question 917520
The amount that each one has at any tine
is a linear ( straight line ) relation.
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Let {{{ y }}} = total that each one has at any time
Let {{{ x }}} = number of weeks after they each started
adding money to their initial deposits
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Sam's equation:
{{{ y = 20x + 100 }}}
Jack's equation:
{{{ y = 10x + 180 }}}
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Just set the y's equal to each other
{{{ 20x + 100 = 10x + 180 }}}
{{{ 10x = 80 }}}
{{{ x = 8 }}}
In 8 weeks they will have the 
same amount of money:
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Here are the plots of their equations:
{{{ graph( 400, 400, -1, 10, -30, 300, 20x + 100, 10x + 180 ) }}}