Question 1112105
Let {{{ E }}} = weekly earnings
Let {{{ n }}} = number of cell phones sold
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Equation for Alan:
(1) {{{ E = 40n + 200 }}}
Equation for Joel:
(2) {{{ E = 55n }}}
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These are straight line equations that meet
at a single point. Notice that {{{ n }}} must be 
a whole number, since they can't sell part of a cell phone
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Make the earnings, {{{ E }}} equal to eachother
{{{ 40n + 200 = 55n }}}
{{{ 15n = 200 }}}
{{{ n = 13.333 }}}
The nearest whole number is {{{ 13 }}}. Joel has to sell
one more, or {{{ 14 }}} phone/wk in order to make
more money than Alan
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check the answer:
{{{ n = 14 }}}
(1) {{{ E = 40n + 200 }}}
(1) {{{ E = 40*14 + 200 }}}
(1) {{{ E = 560 + 200 }}}
(1) {{{ E = 760 }}}
and
(2) {{{ E = 55n }}}
(2) {{{ E = 55*14 }}}
(2) {{{ E = 770 }}}
So, Joel makes $10/wk more than Alan