Sherlock Holmes vs. Professor Moriarty

Logic Level 5

"Here is a list of the first few house numbers that Professor Moriarty has broken into in Baker Street on consecutive nights, Holmes." said Watson, passing the list to Holmes.

Watson looks by his right foot and notices a little note. He reads the note to Holmes, which the note says,

"I will only intend to rob houses for just this month; the month of July. Even though I will not steal from every house every night, it is still 1 day for 1 house. I will let you know on this thing, if you ever make it to Day 8, think of "one less number" to deal with". The fun fact is that there is a house that is numbered “0”, who would have thought? Anyways, you may be smart Holmes and Watson, but not smart to find me in any of these 32 house numbers. " - Professor Moriarty

Holmes studies the list for a moment and quickly supplied Watson with an answer.

From the list of house numbers below, can you give the last day which Professor Moriarty intends to rob during the month of July?

5, 20, 24, 6, 2, 8,…

The answer is 12.

1 solution

Lew Sterling Jr
Aug 29, 2015

Okay, can you please explain where did you get the 3 from in Day 8 (i.e., 12 / 3 = 4)? Following the logic of the first 5 numbers, this is what I got:

1) 5 * 4 = 20

2) 20 + 4 = 24

3) 24 / 4 = 6

4) 6 - 4 = 2

5) 2 * 4 = 8

6) 8 + 4 = 12

7) 12 / 4 = 3

8)** 3 - 4 = -1

Day 7, thus, should be the last day. However, the ambiguity of the question seems to suggest that the house number doesn't follow the standard rules of having only positive numbers (i.e., it can contain negative numbers). It means that day 31 should be the last day as 32 obviously doesn't exist in July.

Please explain.

A Former Brilliant Member - 5 years, 9 months ago

True. Take a quick look at Professor Moriarty's note.

Lew Sterling Jr - 5 years, 9 months ago

I missed that line...but is it possible to add a line stating that it can't be negative house number?

A Former Brilliant Member - 5 years, 9 months ago

@A Former Brilliant Member – Have you seen -1232 Williams Street? Sounds like you almost answered your own question.

Lew Sterling Jr - 5 years, 9 months ago

@Lew Sterling Jr – Don't know whether you've actually read my first comment: The ambiguity of the question seems to suggest that the house number doesn't follow the standard rules of having only positive numbers (i.e., it can contain negative numbers. To further explain my statement, if zero house number exists, then this is a fiticious world where house numbers may not follow our real worlds rule, therefore the existence of negative house number is possible. I'm sorry if this offended you, because you seem rather, defensive.

A Former Brilliant Member - 5 years, 9 months ago

@A Former Brilliant Member – This basically was suppose to be a riddle technically.

Lew Sterling Jr - 5 years, 9 months ago

@Lew Sterling Jr – How do we know that the "one less number to deal with" is not continued after the eighth day?

Saya Suka - 2 years ago

@Saya Suka –

"I will let you know on this thing, if you ever make it to Day 8, think of "one less number" to deal with"" is just a reference to only Day 8 based on the wording of the problem.

Lew Sterling Jr - 2 years ago

But the number 12 isn't in the list

Gurman Garg - 2 years, 8 months ago

Sherlock Holmes vs. Professor Moriarty

The answer is 12.

1 solution

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