When will the candle burn out copmletely

Question

A candle was lit at 7 o'clock. At 9:15 it has a lengthof 12 cm. At 11:45, its length is only 8 cm. When is the candle completely burned ?

Answer 1

Assuming the candle burns at a constant rate, here are two ways of looking at this and you can decide which you prefer:

 

From 9!15 to 11:45, 2.5 hours have passed and 4cm of the candle has burned. (12 cm - 8cm)

 

After another 2.5 hours, another 4 cm will have burned. It will be 2:15 and the candle will be 4 cm.

 

After another 2.5 hours, the last 4 cm will have burned. It will be 4:45.

 

Or  the problem could be solved by setting up ratios.

 

2.5/4 = x/8  to show that if 4 cm burns in 2.5 hours then how long will it take to burn the last 8 cm

 

cross mulitply and you get 4x =20 so x =5 

 

meaning it will take another 5 hours

 

add 5 hours to 11:45 and you get 4:45