A candle of 6 cm long burns at the rate of 5 cm in 5 hour and an another candle 8 cm long burns at the rate of 6 cm in 4h. What is the time required to each candle to remain of equal lengths after burning for some hours, when they starts to burn simultaneously with uniform rate of burning?

Explanation:-

(6 - x) = (8 - 1.5x)
Or, x = 4cm.
So, It will take 4 hours to burn it in such a way that they will remain equal in lengths.