Plan A function: y = .04x + 4.00
The rate is 4 cents per message, the variable x is the number of messages, the height above the origin is 4 dollars.
Plan B function: y = .05x
The rate is 5 cents per message, the variable x is the number of messages, the height above the origin is zero.
If you plan to send 360 messages, the cost for Plan A is $18.40. (plug 360 into the function)
If you plan to send 360 messages, the cost for Plan B is $18.00.
Choose Plan B because it's cheaper.
If you plan to send 500 messages, the cost for Plan A is $24.00. (plug 500 into the function)
If you plan to send 500 messages, the cost for Plan B is $25.00.
Choose Plan A because it's cheaper.
The domain for both plans is x > 0 and x is a whole number.
The range for Plan A is y > 4.00
The range for Plan B is y > 0
The graph of Plan B shows direct variation because the line passes through (0,0).
The graph of Plan a does not show direct variation.
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