Question

Two candles of equal length starts burning at the same instant. One of the candles burns in 5 hours.and other in 4 hrs. By the time one candle is 2 times the length of the other. The candles have already burnt for how much time?

Answer 1

Answer:

3 hrs 20 minutes

Step-by-step explanation:

Let say Length of Each Candle = 20L  

One Candle burn in 5 hr

so burning rate = 20L/5  = 4L /hr

Another candle burn in 4 hrs

so burning Rate =  20L/4 = 5L / hr

Let say after T hrs  one candle is 2 times the length of the other

one candle  burnt in T hrs =  4LT

Remaining Candle = 20L - 4LT

other candle burnt in T hrs = 5LT

other Candle Remaining = 20L - 5LT

20L - 4LT = 2 * (20L - 5LT)

=> 20 - 4T = 2 * (20 - 5T)

=> 20 - 4T = 40 - 10T

=> 6T = 20

=> 3T = 10

=> T = 10/3

Both candles have burnt for 10/3 = 3.33 hrs = 3 hrs 20 minutes