I'm trying to review for the GRE general test and haven't done any "real" math in about 4 years...These permutations and combinations questions have me stumped. How would you solve the following (I have the answers, I just don't know how they got them):

1. "How many 3-digit positive integers are odd and do not contain the digit "5"?
(Answer: 288)

2. "From a box of 10 light bulbs, 4 are to be removed. How many different sets of 4 bulbs could be removed?"
(Answer 210)

Really appreciate the help!

1. "How many 3-digit positive integers are odd and do not contain the digit "5"?
(Answer: 288)

how many different digits can be in the hundreds place? (example: the 7 in 728)? 1, 2, 3, 4, 6, 7, 8 and 9 so 8 different digits.

how many different digits can be in the tens place? (example: the 2 in 728)? 0, 1, 2, 3, 4, 6, 7, 8 and 9 so 9 different digits again.

Now, the ones place can be 1, 3 7 or 9 so that is 4 different digits.

8 * 9 * 4 = 288

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1. For the three digit number the first digit could be any number from 1 thru 9 excluding 5. . So the first digit could be filled in 8 different ways

the second digit could be 0 thru 9 excluding 5 . So the second digit could be filled in 9 different ways

The last digit can be 1,3,7,9 . So the last digit could be filled up in 4 ways.

So the different combination possible is 8*9*4 = 288 odd positive integers that does not have 5