Thrifty numbers Part 3

Logic Level 1

+ = = × = ÷ = \large{ \square \, + \, \square \, = \, \square \\ \square \, - \, \square \, = \, \square \\ \square \, \times \, \square \, = \, \square \\ \square \, \div \, \square \, = \, \square \\ }

Given that the integers 1 , 2 , , 9 1,2,\ldots,9 are to be filled in all the twelve square boxes above such that all four equations above are satisfied.

What is the maximum possible of distinct number of integers used?

Details and Assumptions

  • You can use the same integer more than once.

  • You are not required to use all nine integers.

  • Each square box can only fill in exactly one digit.

7 9 6 8

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6 solutions

Lu Chee Ket
Dec 8, 2015

One example is sufficient to support the fact of maximum of 9 distinct integers:

1 + 7 = 8 \boxed{1} + \boxed{7} = \boxed{8}

9 5 = 4 \boxed{9} - \boxed{5} = \boxed{4}

2 × 3 = 6 \boxed{2} \times \boxed{3} = \boxed{6}

8 ÷ 4 = 2 \boxed{8} \div \boxed{4} = \boxed{2}

Full set applied. The last row is flexible!

Answer: 9 \boxed{9}

Great! Thank you for your solution.

Chung Kevin - 5 years, 6 months ago

Does 'distinct' mean only used once in the solution? In the above solution , the digit 2 is used twice, therefore it is not distinct, so the answer is 8 ( 8 distinct digits)

Steph Young - 4 years, 10 months ago

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I agree. The word 'distinct' implies this to me and confuses the reader. There is too much necessary mind reading in some of the problems. Too many ways to read them. It should be clear what is meant before it is published here as a problem.

Eric Jones - 2 years, 3 months ago
Akhil Bansal
Dec 8, 2015

8 + 1 = 9 7 5 = 2 4 × 2 = 8 6 ÷ 3 = 2 \large{ \boxed{8} \, + \, \boxed{1} \, = \, \boxed{9} \\ \boxed{7} \, - \, \boxed{5} \, = \, \boxed{2} \\ \boxed{4} \, \times \, \boxed{2} \, = \, \boxed{8} \\ \boxed{6} \, \div \, \boxed{3} \, = \, \boxed{2} \\ } It is clearly seen, that I have used all the given digits.

Great! Thank you. To be honest, I actually struggled to fit all 9 numbers inside. haha :)

Chung Kevin - 5 years, 6 months ago

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Welcome! ,I have also solved part 1 and 4 but can't post solution there due to some problem on my brilliant page.

Akhil Bansal - 5 years, 6 months ago

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Hmmm... That's weird. @Brilliant Mathematics can you look into this? Thank you.

Chung Kevin - 5 years, 6 months ago
John Wyatt
Dec 9, 2015

By example

3+4=7

9-4=5

2x3=6

8/1=8

Yet another solution with all 9 9 digits.

2 + 4 = 6 8 3 = 5 3 × 3 = 9 7 ÷ 1 = 7 \large{ \boxed{2}\,+\,\boxed{4}\,=\,\boxed{6}\\ \boxed{8}\,-\,\boxed{3}\,=\,\boxed{5}\\ \boxed{3}\,\times\,\boxed{3}\,=\,\boxed{9}\\ \boxed{7}\,\div\,\boxed{1}\,=\,\boxed{7}\\ }

Another great solution. Thank you!

Chung Kevin - 5 years, 6 months ago

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A more tough problem would have been having an added restriction of using only three of the four equations. You fill only 9 blanks then. Can you fit in all 9 numbers?? (Though this is also solved by Lu Chee Ket in the solution)

Janardhanan Sivaramakrishnan - 5 years, 6 months ago

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That is good question too, but it appears to contrived because it has too many constraints. And it may come off as too complicated.

Let me see how to make more variations of these problems.

Chung Kevin - 5 years, 6 months ago
Nadia Khan
Feb 15, 2016

Well as the puzzle had stated, "What is the maximum possible distinct number of integers used?" It would be quite logical that the answer would be 9 without any work needed as you were given numbers from 1 to 9. 0 does not count so you only have 9 numbers that are available. You were given details and assumptions so there is a chance that some of the statements given were false.

Joe DeAlmo
Dec 14, 2015

I found it easiest to start with the division problem and work up. My solution:

5 + 4 = 9 \boxed{5} + \boxed{4} = \boxed{9} 6 3 = 3 \boxed{6} - \boxed{3} = \boxed{3} 7 × 1 = 7 \boxed{7} \times \boxed{1} = \boxed{7} 8 ÷ 4 = 2 \boxed{8} ÷ \boxed{4} = \boxed{2}

Yay! Thank you for your solution

Chung Kevin - 5 years, 6 months ago

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