Question 173784
Your cell phone plan charges you $.02 to send a text message and $.07 to receive a text message. You plan to spend no more than $5 a month text messaging.
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a. Write an equation in standard form that models the possible combinations of sent text messages and received text messages.
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Let x = messages received
let y = messages sent
:
.07x + .02y = 5
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b. Graph the equation from part (a). Explain what the intercepts of the graph mean in this situation.
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convert equation to the general form
.02y = 5 - .07x
y = {{{5/.02}}} - {{{.07/.02}}}x
y = 250 - 3.5x
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Plot these two points
 x | y
-------
20 |180
60 | 40
Your graph should look like this:
{{{ graph( 300, 200, -10, 90, -100, 300, 250-3.5x) }}}
Note: y axis are the no. messages sent, x axis are the no. of messages received
;
The y intercept (250) means only sent messages, none received (x=0) 
The x intercept, approx 71 messages received, none sent (y=0)
:
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c. List three other possible combinations of the number of messages you can send and receive.

you can do this;
You can get the approximate x/y values from the graph or; 
To be exact, choose a value for x and find y in the above equation
:
Did this make sense to you. Any questions?