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math problem


Ramsey

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michelle dropped her iphone and the screen cracked. she can no longer read the last four digits of anyones number. the last 4 digits of caseys phone number could include 1,2,5,6,8, or 9. if michelle knows that the first digit is NOT 5, the last digit is odd and no digits are repeated, what are the maximum # of phone calls michelle would have to make to call casey.

 

at first i thought 156

 

but im thinking its 120

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I figured it by looking at the last number combinations:

 

If it is 1, there are 48 permuations.

5, 60 and 9, 48.

 

48+60+48 = 156

 

This.

If 156 is not an option I would question if the problem was copied correctly.

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I figured it by looking at the last number combinations:

 

If it is 1, there are 48 permuations.

5, 60 and 9, 48.

 

48+60+48 = 156

 

There are 48 different inputs for each last number, there are only 3 numbers that could be last.

 

48+48+48 = 144

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There are 48 different inputs for each last number, there are only 3 numbers that could be last.

 

48+48+48 = 144

 

If you use 5 for the last number there are 60 options for the first 3.

If you use 1 or 9 there are 48 options for the first 3.

 

Hence the 48+60+48=156

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