A 3-inch candle burns down in 6 hours. Assuming the candles are the same thickness and make (that is, directly proportional), how long would it take a 4-inch candle to burn down?
Since the candles are of the same make and thickness, you can assume the rate of burning is constant. This means that the time it takes for a candle to burn is directly proportional to the length of the candle.
A 3-inch candle takes 6 hours to burn down completely, so you can set up a proportion to find out how long it would take a 4-inch candle to burn.
3 inches / 6 hours = 4 inches / x hours
Now, solve for x:
(3 inches / 6 hours) = (4 inches / x hours)
3/6 = 4/x
3x = 4 * 6
3x = 24
x = 24 / 3
x = 8
So, a 4-inch candle would take 8 hours to burn down completely.