Permutation and Combiniation

1.Each seat in the corent hall is labelled with the upper case letter followed by a positive integer 100 to 999.Using this labelling system,what is the greatest number of seats can be labelled?

2.How many ways can a black, a red,a green,a blue,a yellow and a purple marble be arranged in a row if the black and the purple marbles must be placed at the two ends of the row?

3.if 4 fair dice are thrown,find the number of outcomes which have at least one"6"?