slope/intercept

Question

5) You buy your friend a $50 gift card to download music. Each song downloaded costs $1.25. She wants to keep track of how much money she has left on the gift card as she purchases music. a) What is the slope in this situation and what does it represent? b) What is the y-intercept and what does it represent?

Answer 1

y = mx + b

If I start with $50 and subtract $1.25 for each song, that looks like...

y = 50 - 1.25x

Of course, we have to turn things around.

y = -1.25x + 50

The slope is -1.25, the declining value of the gift card as she buys songs.

The y-intercept is 50, the starting value of the gift card.

Just for fun, can you tell me what the next point is?