Problem 1
x = number of weeks
y = amount left on gift card (in dollars)
He starts with $100. Then each week he spends $4.99 which means we subtract 4.99x from the 100 mentioned. We form the expression 100 - 4.99x which is the same as -4.99x + 100
The equation y = -4.99x + 100 is in slope intercept form with m = -4.99 as our slope and b = 100 as the y intercept.
Answer: y = -4.99x + 100
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Problem 2
The y intercept is 100 because it's the starting amount. Mark the point (0,100) on the graph.
We need one more point to form a straight line. Let's say we picked something like x = 4 to plug into the equation found earlier
y = -4.99x + 100
y = -4.99*4 + 100
y = -19.96 + 100
y = 80.04
After x = 4 weeks, Mark has y = 80.04 dollars left on the card. We'll plot the point (4, 80.04). Then we connect those points with a straight line.
Check out the diagram below.
The location of (4, 80.04) can be visually marked as (4,80) since it's close enough in my opinion.
