QR question

[kov82]

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How many 3-digit positive integers are odd and do not contain the digit “5”?

its 288, but how do you do it?

 

[Vicviper]

Wow, that's a tricky one.. ok, lets see... here are some rough numbers as I'm going through this in my head,

3 digit, so that's 1-999, and then odd, so that leaves us with 500 numbers.

Taking out all of the ones in the 500's, that leaves us with 450... all the ones with 5 in it's ones digit, that gets rid of 20% of them... so that's 360,

all of the ones with 5 in the 10's digit, so that gets rid of another 10% of that... so that leaves me with 324... hm.

Long story short, I didn't run into ANY of these types on my DAT, so I wouldn't worry about it too much, hehe. Though if you can do this in under 30 seconds or so I give you props. 😀

 

[purplepanda]

Wow, that's a tricky one.. ok, lets see... here are some rough numbers as I'm going through this in my head,

3 digit, so that's 1-999, and then odd, so that leaves us with 500 numbers.

Taking out all of the ones in the 500's, that leaves us with 450... all the ones with 5 in it's ones digit, that gets rid of 20% of them... so that's 360,

all of the ones with 5 in the 10's digit, so that gets rid of another 10% of that... so that leaves me with 324... hm.

Long story short, I didn't run into ANY of these types on my DAT, so I wouldn't worry about it too much, hehe. Though if you can do this in under 30 seconds or so I give you props. 😀

good way of looking at it.

 

[Streetwolf]

How many 3-digit positive integers are odd and do not contain the digit "5"?

its 288, but how do you do it?

For the first digit there are 8 possibilities (1-4, 6-9).
For the second digit there are 9 possibilities (0-4, 6-9).
For the third digit there are 4 possibilities (1, 3, 7, 9).

So 8 * 9 * 4 = 288.

You may now issue said props.

 

[Vicviper]

Super Props!

 

[drpharMD]

That's amazing. Where did you get this problem (real DAT or practice test)?

 

[kov82]

thanks for replying guys, I probably should have mentioned it was a probability problem, I got it off a GRE book.