Question

Sukriti has two candles of the same length, one of which burns down in 4 hours, and the other in 7. If she lights both the candles at midnight, then at what point of time would the length of one candle be twice as long as the other?

• A. 2 hours 18 minutes
• B. 1 hour 48 minutes
• C. 2 hours 48 minutes
• D. 3 hours 18 minutes

Answer 1

The correct option is C 2 hours 48 minutes

Let the length of the candles be L and the time taken for each candle to become twice as long as the other be T hours.

Taking the candle which burns in 4 hours:

Length burning in 4 hours = L
Length burning in T hours = (TL/4)
So, Length of the candle left to burn = L - (TL/4)

Similarly, for the candle which burns in 7 hours:

Length burning in 7 hours = L
Length burning in T hours = (TL/7)
So, Length of the candle left to burn = L - (TL/7)

Now according the question:
L - (TL/7) = 2 x {L - (TL/4)}
T/2 - T/7 = 1
5T/14 = 1
T = 14/5
= 2 hours 48 minutes