Manish travels at the speed of 40 km/hr for 3 hours and the speed of 60 km/hr for 4.5 hours. In this way he covers three fifths of the total distance. At what average speed should he travel to cover the remaining distance in 4 hours ?
The difference between a two-digit number and the number obtained by interchanging the two digits of the number is 9. If the sum of the two digits of the number is 15, then what is the original number ?