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IrinaOK
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I have the OE, but still do not understand it. Thank you. 21 Sep 2007, 16:11
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Please explain your answer...

I have the OE, but still do not understand it.

Thank you.

A 40
B 56
C 72
D 81
E 104



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Ravshonbek
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I have the OE, but still do not understand it. Thank you. 21 Sep 2007, 16:34
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IrinaOK
Please explain your answer...

I have the OE, but still do not understand it.

Thank you.

A 40
B 56
C 72
D 81
E 104
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looks like 72, C
takes more than 2 mins.
i might be missing smth, but there should be shorter method to come to the right answer.
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bkk145
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I have the OE, but still do not understand it. Thank you. 21 Sep 2007, 17:26
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IrinaOK
Please explain your answer...

I have the OE, but still do not understand it.

Thank you.

A 40
B 56
C 72
D 81
E 104
Show more


C for me
Say if ABC is the three digits integer
Then count the numbers that have the same digit.

8B8 => Total of 10
88C => Total of 10-1 =9 (minus one because you already count 888 in the first one)
8BC where BC = 00, 11, 22, and so on without 88, so this is total of 9

10+9+9 = 28
Same for 900s, so you have 28*2 = 56
200 - 56 = 144
Only odd, so 144/2 = 72
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Skewed
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I have the OE, but still do not understand it. Thank you. 21 Sep 2007, 22:02
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3 digit odd number ABC greater than 800, in which none of digits are repeated.
0-9= 10 digits

A= you have a choice of 8 or 9
C= you have a choice of 1,3,5,7,9
B = you have a choice of 8 unused digits

Case where A= 8:

A= 1 choice of digit (8 only)
C= 5 choices (1,3,5,7,9)
B= 8 choices (as you can not use A or C again)

so A*B*C= 1*8*5=40

Case where A=9:

A= 1 choice of digit (9 only)
C= 4 choices (1,3,5,7)
B= 8 choices (as you can not use A or C again)

so A*B*C= 1*8*4=32

There are 40+32= 72 choices of a three digit odd integer greater than 800 that contains 3 distinct digits.
[/b]
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KillerSquirrel
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I have the OE, but still do not understand it. Thank you. 23 Sep 2007, 05:05
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Using the probability method

N = 1,000 – 800 = 200

When 8 is the first digit choosen (i.e. 8xx)

P1 = 9/10*5/10 = 45/100 ---> when the second digit is even.
P2 = 9/10*4/10 = 36/100 ---> when the second digit is odd.

When 9 is the first digit choosen (i.e. 9xx)

P3 = 9/10*4/10 = 36/100 ---> when the second digit is even.
P4 = 9/10*3/10 = 27/100 ---> when the second digit is odd.

SUM(P) = (45/100+36/100+36/100+27/100)/4 = 36/100

N*P = 200*36/100 = 72

:)



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Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Problem Solving (PS) Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
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