Question

When a window is open, the temperature in a room falls 5ºF every 15 minutes. Before the window is opened, the temperature was ​ 70ºF​ .

Use the Ray tool to make a graph that shows the temperature of the room, T, after the window has been open for m minutes.

Answer 1

You get a linear decrease of 5°F every 15 minutes, so the rate is -5/15 = -1/3 °F per minute. The temperature T (in °F) after m minutes is

T(m) = 70 − (1/3)m, for m ≥ 0.

To draw the ray (using the Ray tool):
- Start point: (0, 70).
- Another point on the ray: (15, 65) (because 70 − (1/3)·15 = 65).
- Draw the ray through those points extending to the right (m increasing).

You can check more points: (30, 60), (45, 55), etc. The ray shows a straight line with y-intercept 70 and slope −1/3, defined for m ≥ 0.