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Logic Level 1

I have 3 distinct positive integers.
The sum of these three integers is either 5, 6 or 7.
The product of these three integers is either 8, 9 or 10.

What is the median of these three integers?


Inspiration .

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4 solutions

Pranshu Gaba
Apr 8, 2016
  • Five cannot be written as the sum of three distinct positive integers.

  • The only way to write six as a sum of three distinct positive integers is { 1 , 2 , 3 } \{1, 2, 3 \} \implies product = 6.

  • The only way to write seven as a sum of three distinct positive integers is { 1 , 2 , 4 } \{1, 2, 4 \} \implies product = 8.

Since the product cannot be 6, the product is 8. Therefore the numbers are { 1 , 2 , 4 } \{1, 2, 4\} and the median is the central value, that is 2 \boxed{2} _\square

Moderator note:

Good clear explanation!

While it is true the product must be 8, this is not even necessary to consider. The problem can be solved from the first condition only, because the median is 2 whether the sum is 6 or 7.

Thomas N Dowling - 4 years, 8 months ago

"The only way to write seven as a sum of three distinct positive integers is product = 8." Wait you say "to write seven" then you equal it to 8? ("=> product =8") Is this a typo or I just didn't get it?

David Movsisyan - 3 years, 7 months ago

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Sorry if I was not clear. 7 = 1 + 2 + 4. The product of 1, 2, and 4 is 8.

Pranshu Gaba - 3 years, 7 months ago

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Ohk got ya now, thanks ;)

David Movsisyan - 3 years, 7 months ago

I do not get it. 1+2+4=7 but 1+2+4 does not equal 8

Zoie For - 3 years, 2 months ago

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The sum is 1 + 2 + 4 = 7 1 + 2 + 4 = 7 , and the product 1 × 2 × 4 1 \times 2 \times 4 is 8.

Pranshu Gaba - 3 years, 2 months ago

Sum is 7 = 1 + 2 + 4. (i.e. Sum => add the numbers together) Product is 8 = 1 * 2 * 4. (i.e. Product => multiple the numbers together)

Patrick Farley - 2 years, 4 months ago
Andrew Tawfeek
Apr 8, 2016

For it to be a product of one of those three integers, you must look at its factors. Decomposing each into its primes:
8 = 4x2x1 = 2x2x2x1,
9 = 3x3x1, and
10 = 5x2x1.


Looking at the prime factorization of these numbers, only one of them has a sum of factors between 5 and 7 and has them all be distinct. The factors of 8. So the three numbers are 1, 2, and 4. The median is 2.

Moderator note:

Good clear explanation!

But why do all factors have to be distinct? Edit: Oh!! I just saw it in the question! 'three DISTINCT positive integers' sry must've just glossed over it not knowing its meaning. Your solution made me awear of what 'distinct' factors were, so thank you for that %)

Ded fekuff - 2 years, 9 months ago

Hey 9 is not 3×2×1. Its 3×3×1

Vignesh S - 5 years, 2 months ago

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My mistake, fixed.

Andrew Tawfeek - 5 years, 2 months ago
Aris Adriano
Apr 25, 2019

I went with the process of elimination. (1,2,3) has a sum of 6. However its product of 6 does not meet the criteria. The only possible combination is (1,2,4) because of its sum of 7 and product of 8, which both meet the criteria.

Nihar Mahajan
Apr 8, 2016

Let the integers be a , b , c a,b,c . then we have a b c abc as 8 or 9 or 10. since minimum value of a b c = 8 abc=8 , then at least one of them is 1 1 . Suppose a = 1 a=1 . Since maximum of a + b + c a+b+c is 7 7 and b c bc can be 8 or 10 we have ( b , c ) = { ( 2 , 4 ) , ( 2 , 5 ) } (b,c)=\{(2,4),(2,5)\} but if we have ( 2 , 5 ) (2,5) is considered, a + b + c = 1 + 2 + 5 = 8 > 7 a+b+c=1+2+5=8>7 thus ( 2 , 4 ) (2,4) is only possible. Hence ( a , b , c ) = ( 1 , 2 , 4 ) (a,b,c)=(1,2,4) which have 3 3 terms. Thus median term = 3 + 1 2 = 2 =\dfrac{3+1}{2}=2 and the second term in 1 , 2 , 4 1,2,4 is 2 \boxed{2} which is the median.

Moderator note:

I disagree with this sentence as it is phrased.

Since minimum value of a b c = 8 abc=8 , then at least one of them is 1 1 .

Note that if we had a b c = 30 abc = 30 (because all that you're using is the minimum), then the statement is false.

What about 1,3,3? No one said the integers were all different. Right?

Joseph Mbogori - 3 years, 7 months ago

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"distinct"?

Ehab Salam - 3 years, 6 months ago

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