Question

A 10 inch-candle burns at a linear rate. It measures 9 inches two hours after it was lit. Which equation can be used to find the length of the candle, y, in inches after x hours it was lit?

1. y = 10 - 0.5x
2. y = 10 - 4.5x
3. y = 10 - 9x
4. y = 10 - 2x

Answer 1

• 1. y = 10 - 0.5x

Explanation:

Find the burning rate of candle per hour:

• (10 - 9)/2 = 1/2 = 0.5 in

The rate is the slope of the linear function and the initial length of the candle is the y-intercept:

• m = - 0.5,
• b = 10.

The equation is:

• y = -0.5x + 10 or
• y = 10 - 0.5x

Correct choice is the first one.