To travel 720 km, a Express train takes 6 hours more than Duronto. If however, the speed of the Express train is doubled, it takes 2 hours less than Duronto. The speed of Duronto (in km/hr) is?
If on a Sale there is 40% discount on the marked price of Rs 1000, but the sale is done at Rs 510 only then what additional discount (in %) did the customer get?