4/19/10

Test 7 Section 7 - #13 (page 787)

Remember our conditions:

  • One number is odd.
  • One number is a multiple of 5.
  • One number is the day of the month of Kyle's birthday.


The key is the part where they say that each number satisfies exactly one of the conditions.  That means, for example, if the number 15 were in a combination, we'd have to eliminate that choice, because 15 is both odd and a multiple of 5.  It satisfies 2 conditions, but the question said that's not allowed.  We can actually eliminate 3 choices just because of this: (B), (C), and (D) all have odd multiples of 5 (25, 15, and 15, respectively).


(A) 14-20-13
(B) 14-25-13
(C) 15-18-16
(D) 20-15-20
(E) 34-30-21

So how do we know whether to pick (A) or (E)?  Well, if it were (E), our odd number would be 21, our multiple of 5 would be 30, and that'd mean our day of the month would have to be 34.  But no month has 34 days.  So we have to pick (A): 13 is odd, 20 is a multiple of 5, and 14 is a day of the month.

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