hey mathematicians, I need some help with permutations and probability

1. How many ways can you arrange the letters in the world DEPRESSING

a) without restriction

This one is easy. 10!/2!x2! = 907200

b) What is the probability that the S is the last letter?

Can't do this one. The answer is 1/10. (NOTE: There are two S's and two E's.)

2. How many ways can you arrange the numbers 1 2 3 4 5 6 7 8 9 so that the odd numbers appear in ascending order?

3. A spinner is has parts A B C D E on it so that the probability of spinning on any letter is 1/5. (equally likely). Hence the probability of spinning A, B, C, D and E is 20%. How many times does the spinner have to be spun so that Michael can say that the chances of having at least one E is 99%?I don't get this. The probability of a 1 is 50%. Does that mean the probability for each of the numbers will be (100 - 50)/5 = 10% for the other numbers. If so, then the chances of rolling a six will be 10%.

4. A dice has numbers 1 2 3 4 5 6 on it. It is biased so that the probability of rolling a 1 is 50% and equally likely to roll on the other numbers. What is the probability of rolling a six?

What do you think?

THANKS GENIUSES