Question 1025108
(a) if repetition are allowed then _ _ _ _ _  in the first space we have only 9 choice as 0 cant be considered.  and for all rest 4 space we have 10 choices.... so answer becomes 9*10^4.

(b)when repetition are not allowed thn _ _ _ _ _   for the 1st space we have 9 choice.... and now we use the formula for we have to select 4 out of 9 which is 9p4 and the answer becomes 9*9*8*7*6.