blackmangotree
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Okay so i have a test and they're literally giving us questions that are HARD AF. I have no idea what to do for this question:

Bill and Sue are making 4-digit codes. The digit 0 is NOT used. Bill only uses odd digits and Sue only uses even digits.

a) Bill can make x more codes than Sue. Assume that the digits CAN NOT be repeated. Work out the value of x

b) In fact, the digits can be repeated, what does this tell you about the actual value of x? (i.e: is it bigger, smaller or the same?)

Thank you very much guys
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Rufus the red
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(Original post by blackmangotree)
Okay so i have a test and they're literally giving us questions that are HARD AF. I have no idea what to do for this question:

Bill and Sue are making 4-digit codes. The digit 0 is NOT used. Bill only uses odd digits and Sue only uses even digits.

a) Bill can make x more codes than Sue. Assume that the digits CAN NOT be repeated. Work out the value of x

b) In fact, the digits can be repeated, what does this tell you about the actual value of x? (i.e: is it bigger, smaller or the same?)

Thank you very much guys
Is this a test you're doing now? If so I don't think it would be a good idea to ask for help as it may skew your results.
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blackmangotree
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(Original post by Rufus the red)
Is this a test you're doing now? If so I don't think it would be a good idea to ask for help as it may skew your results.
Its not a real test its just on mathswatch x
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Rufus the red
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(Original post by blackmangotree)
Its not a real test its just on mathswatch x
In that case:
There are 9 digits that they can choose from (1,2,3,4,5,6,7,8,9). Look at how many of them are odd and how many are even and think about how if the two people are restricted to one set it may alter the pool of numbers they can choose from.
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RogerOxon
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(Original post by blackmangotree)
Okay so i have a test and they're literally giving us questions that are HARD AF. I have no idea what to do for this question:
You can do this - you just need to think about it enough to understand it.

b. For each of the digits in the combination, how many options are there? In this part, it's the same for each digit in the combination. If you have n possible choices for each, then how many do you have overall?

a. Exactly the same approach as for b. What does not being able to reuse a digit change?

EDIT: Had a and b the wrong way around
Last edited by RogerOxon; 6 months ago
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blackmangotree
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(Original post by RogerOxon)
You can do this - you just need to think about it enough to understand it.

a. For each of the digits in the combination, how many options are there? In this part, it's the same for each digit in the combination. If you have n possible choices for each, then how many do you have overall?

b. Exactly the same approach as for a. What does not being able to reuse a digit change?
So for Bill, he can chose from the numbers 1, 3, 5, 7, 9
For Sue, she can chose from 2, 4, 6, 8

so because they can only make a 4-digit code, I did:

Bill: (he has five options) so 5x5x5x5 = 625
Sue: (she has 4 options) so 4x4x4x4 = 256

Then i did 625 - 256 to get 369 but it's saying that it's wrong?
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blackmangotree
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(Original post by Rufus the red)
In that case:
There are 9 digits that they can choose from (1,2,3,4,5,6,7,8,9). Look at how many of them are odd and how many are even and think about how if the two people are restricted to one set it may alter the pool of numbers they can choose from.
Thank you so much for your help, this was my thought process trying to answer it:

for Bill, he can chose from the numbers 1, 3, 5, 7, 9
For Sue, she can chose from 2, 4, 6, 8

so because they can only make a 4-digit code, I did:

Bill: (he has five options) so 5x5x5x5 = 625
Sue: (she has 4 options) so 4x4x4x4 = 256

Then i did 625 - 256 to get 369 but it's saying that it's wrong?
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Rufus the red
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(Original post by blackmangotree)
Thank you so much for your help, this was my thought process trying to answer it:

for Bill, he can chose from the numbers 1, 3, 5, 7, 9
For Sue, she can chose from 2, 4, 6, 8

so because they can only make a 4-digit code, I did:

Bill: (he has five options) so 5x5x5x5 = 625
Sue: (she has 4 options) so 4x4x4x4 = 256

Then i did 625 - 256 to get 369 but it's saying that it's wrong?
For the first part it says that numbers can't be repeated but you're otherwise on the right track.
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RogerOxon
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(Original post by blackmangotree)
So for Bill, he can chose from the numbers 1, 3, 5, 7, 9
For Sue, she can chose from 2, 4, 6, 8

so because they can only make a 4-digit code, I did:

Bill: (he has five options) so 5x5x5x5 = 625
Sue: (she has 4 options) so 4x4x4x4 = 256

Then i did 625 - 256 to get 369 but it's saying that it's wrong?
Sorry - I'd misread it - for a the digits cannot be repeated. You're on the right track.
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blackmangotree
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(Original post by RogerOxon)
Sorry - I'd misread it - for a the digits cannot be repeated. You're on the right track.
wait but I haven't repeated any of the numbers tho?
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mqb2766
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(Original post by blackmangotree)
wait but I haven't repeated any of the numbers tho?
If you had 5 choices for the first odd digit, how many for the second, how many for third etc.?
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blackmangotree
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(Original post by mqb2766)
If you had 5 choices for the first odd digit, how many for the second, how many for third etc.?
OMG I just realised thank you so much,

so it would be 5 x 4 x 3 x 2?
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mqb2766
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(Original post by blackmangotree)
OMG I just realised thank you so much,

so it would be 5 x 4 x 3 x 2?
Of course. Just put some numbers in if you don't see the pattern immediately.
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