Answers

2014-06-10T15:37:35+05:30
678 786 867 864 865 687 657 645 654 647 657 648 658  876 875 874 845 854 856 865 867 785 784 756 754 746 748 758 768   
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2014-06-10T15:50:33+05:30
Digits are 4,5,6,7,8 for number to be greater than 600 at the hundred place 6,7,8 appear and this can be done 3 ways .
for remaining tow places we choose two number from remaining four digits. this can be done 4C2 ways = 4!/(2!2!) = 6 and two number can be interchanged by 2! = 2 ways .
so total numbers which is greater than 600 are = 2*3*6 = 36.
if you can not understand please ask. 
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