Thrifty numbers Part 2

Logic Level 2

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

Given that the integers 0 , 1 , 2 , , 9 0,1,2,\ldots,9 are to be filled in all the twelve square boxes above such that all four equations above are satisfied.

What is the minimum possible 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.

4 2 3 1

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5 solutions

Lu Chee Ket
Jan 18, 2016

One example is sufficient to support the fact of minimum of 2 distinct integers:

0 + 0 = 0 \boxed{0} + \boxed{0} = \boxed{0}

0 0 = 0 \boxed{0} - \boxed{0} = \boxed{0}

0 × 0 = 0 \boxed{0} \times \boxed{0} = \boxed{0}

0 ÷ 1 = 0 \boxed{0} \div \boxed{1} = \boxed{0}

Simplest set applied. The last row is flexible!

Answer: 2 \boxed{2}

This is the exact solution I have! Thank you.

Chung Kevin - 5 years, 4 months ago
Akhil Bansal
Dec 8, 2015

0 + 1 = 1 1 0 = 1 0 × 1 = 0 0 ÷ 1 = 0 \large{ \boxed{0} \, + \, \boxed{1} \, = \, \boxed{1} \\ \boxed{1} \, - \, \boxed{0} \, = \, \boxed{1} \\ \boxed{0} \, \times \, \boxed{1} \, = \, \boxed{0} \\ \boxed{0} \, \div \, \boxed{1} \, = \, \boxed{0} \\ } It is clearly seen, that I have used only 2 distinct integers.

Great! What I did was to use 0's for all the boxes except for the second last one.

Chung Kevin - 5 years, 6 months ago

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Can't use just 0's as 0/0 is undefined

John Wyatt - 5 years, 6 months ago

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Yes, that's why I said "except for the second last one". So I've used 0 ÷ 1 = 0 0 \div 1 = 0 .

Chung Kevin - 5 years, 6 months ago

Can you not entirely use 0? Therefore only one integer

Mark Sanders - 5 years, 6 months ago

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I agree. As / the statement 0 is an integer an can satisfy every equation

Don Cartmill - 2 years, 9 months ago

As pointed out, 0/0 is undefined .

Chung Kevin - 2 years, 9 months ago

We are asked about distinct no of integers Basically we selected 0 as base for for every box and has replaced it with 1 in last box So therefore only 1 distinct no I.e. 1 is used instead of base no Therefore ans should be 1

Abi Singla - 3 years, 2 months ago

I agree with Mark . If 0 is an integer You can satisfy all 4 equations with 0

Don Cartmill - 2 years, 9 months ago

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Unfortunately not. Because we cannot devide by zero, therefor 1 must also be used, and a minimum of 2 integers is the answer

Douwe Vanneste - 2 years, 9 months ago
Karl Kalinowski
Jan 1, 2017

Assume that there exists a single integer n that could satisfy every box. Take a look at row 4. n n \frac{n}{n} = n. You cannot divide by zero, so the integer that satisfies this line cannot be zero. We can remove the n factor from the numerator of denominator of n n \frac{n}{n} , giving us 1 1 \frac{1}{1} = n, or just 1 = n. Therefore, if such a number n exists, it must be 1. However, if you replace n for 1 in n + n = n, the first line, this is a contradiction because 1 + 1 does not equal 1. Therefore, no such integer exists in which n could satisfy every box.

It can be proven that there exists a combination of 2 integers that can satisfy the equations by providing an example: 0 + 0 = 0; 0 - 0 = 0; 0 * 0 = 0; 1 / 1 = 1; Therefore, the minimum number of distinct integers is 2.

0 / 0 = 0 therefore only 1 integer required

Don Cartmill - 2 years, 9 months ago

Some one later notes that 0/0=undefined. Actually 0x0 = undefined. However it matters not since 1x1 = 1 Still only 2

Don Cartmill - 2 years, 9 months ago
Denton Young
Jan 1, 2016

What I did:

1 + 1 = 2

2 - 1 = 1

1 x 1 = 1

1 / 1 = 1

Moderator note:

For completeness, since it asks for the minimum, we should show (state) that we cannot just have 1 integer.

Good point. The only way for the first line to have but a single integer is 0 + 0 = 0. But we can't using nothing but 0's since 0 / 0 is undefined. Therefore, a minimum of 2 integers are needed.

Denton Young - 5 years, 5 months ago
Richard Boyd
Jan 1, 2019

"Given that the integers 0,1,2,…,9"

Zero to nine is …….integers. Ten integers, if zero is included. But the problem allows all NINE integers. I guess zero doesn't count? Sort of a no account number. Please excuse the poor excuse for an attempt at mathematical humor.

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