A 9-inch tall candle burns at a rate of 0.4 inches per hour. The height of the candle at any hour is modeled by the equation: c = -0.4t + 9, where c = the height of the candle and t = the time in hours. Find the height of the candle after 2 hours. Also, how long will it take the candle to burn out?

Question

A 9-inch tall candle burns at a rate of 0.4 inches per hour. The height of the candle at any hour is modeled by the equation:  c = -0.4t + 9, where c = the height of the candle and t = the time in hours.  Find the height of the candle after 2 hours.  Also, how long will it take the candle to burn out?

anonymous · Answer

Height of the candle after 2 hours:
where you see a "t" in the equation, replace it with the number "2".  So c = -0.4 * (2) + 9
we see that (-0.4)*(2) = -0.8  so c = 9 -0.8
c = 8.2 inches.

How long take for candle to burn out?  This is another way of asking what is "t" when c=0.

So we plug in:

0 = (-0.4)(t) +9

I'll leave it to you to solve for "t".