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The number 75 can be written as the sum of the squares of 3

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The number 75 can be written as the sum of the squares of 3 [#permalink]

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The number 75 can be written as the sum of the squares of 3 different positive integers. What is the sum of these 3 integers?
A. 17
B. 16
C. 15
D. 14
E. 13

Guys - as the OA is not provided can someone please help me and explain how to solve this?
[Reveal] Spoiler: OA

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Re: Number 75 [#permalink]

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New post 26 Dec 2011, 11:20
The numbers are 5,7, and 1. The answer is Option (E).
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Re: Number 75 [#permalink]

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New post 27 Dec 2011, 03:53
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I think this question has been discussed earlier also.
squares of natural numbers, which are below 75,are 1,4,9,16,25,36,49,64
1+25+49=75 is the only option
so numbers are 1,5,7
sum =13
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Re: Number 75 [#permalink]

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enigma123 wrote:
The number 75 can be written as the sum of the squares of 3 different positive integers. What is the sum of these 3 integers?
17
16
15
14
13

Guys - as the OA is not provided can someone please help me and explain how to solve this?


Responding to a pm.

I think brute force with some common sense should be used to solve this problem.

Write down all perfect squares less than 75: 1, 4, 9, 16, 25, 36, 49, 64.

Now, 75 should be the sum of 3 of those 8 numbers. Also to simplify a little bit trial and error, we can notice that as 75 is an odd numbers then either all three numbers must be odd (odd+odd+odd=odd) OR two must be even and one odd (even+even+odd=odd).

We can find that 75 equals to 1+25+49=1^2+5^2+7^2=75 --> 1+5+7=13.

Answer: E.

Similar question to practice: the-number-90-can-be-written-as-the-sum-of-the-squares-of-128396.html
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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 24 Jan 2012, 18:37
Thanks for a very clear explanation Bunuel.
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Re: Number 75 [#permalink]

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Bunuel wrote:
I think brute force with some common sense should be used to solve this problem.

Write down all perfect squares less than 75: 1, 4, 9, 16, 25, 36, 49, 64.

Now, 75 should be the sum of 3 of those 8 numbers. Also to simplify a little bit trial and error, we can notice that as 75 is an odd numbers then either all three numbers must be odd (odd+odd+odd=odd) OR two must be even and one odd (even+even+odd=odd).


Very elegant solution. I got this question in my GMAT Prep 1. I also figured that it would require brute force. But Bunuel's point about 75 being an odd number and therefore being a sum of either odd-odd-odd or odd-even-even adds an elegant touch to the brute force approach.
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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 18 Apr 2012, 20:11
thanks for the solution... was hoping for another solution other than just brute calculation. bunel you rock tho.
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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 29 Jun 2014, 20:12
is there any way to solve this one faster? I find myself just trying to add the different numbers and spending 3 mins on this questions, just due to the calculations. any tricks on this one? Thanks.
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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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GMAT17325 wrote:
is there any way to solve this one faster? I find myself just trying to add the different numbers and spending 3 mins on this questions, just due to the calculations. any tricks on this one? Thanks.


75 can be expressed as addition of squares of same integer as follows

\(75 = 5^2 + 5^2 + 5^2\)

Leaving one square term as it is; try to search for other options

\(75 = 5^2 + 50\)

Closest is 1 & 49

\(75 = 5^2 + 1 + 49\)

\(75 = 5^2 + 1^2 + 7^2\)

Answer = 5+1+7 = 13 = E
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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 09 Aug 2014, 08:31
I Seriously cannot believe I got this one wrong. I forgot to take into consideration square of 1 is 1 and guessed an answer. Still managed to get a score of 48 on this GMATprep, undeserved if I commit such silly mistakes. Good method Paresh
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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 30 Apr 2015, 02:02
enigma123 wrote:
The number 75 can be written as the sum of the squares of 3 different positive integers. What is the sum of these 3 integers?
A. 17
B. 16
C. 15
D. 14
E. 13

Guys - as the OA is not provided can someone please help me and explain how to solve this?

just pick numbers

most of questions of math test us ability to pick numbers.

not easy one
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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 12 Jun 2015, 00:34
Yeah I misread this question and thought it was asking for factors so I had 5 5 3 which also add up to 13

Oh God.
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The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 10 Jul 2015, 16:48
FatRiverPuff wrote:
Yeah I misread this question and thought it was asking for factors so I had 5 5 3 which also add up to 13

Oh God.


Um...the sum of factors of 75 = 1 + 3 + 5 + 15 + 25 + 75. You just got catastrophically lucky!

Oh God indeed.
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The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 29 Nov 2015, 01:31
enigma123 wrote:
The number 75 can be written as the sum of the squares of 3 different positive integers. What is the sum of these 3 integers?
A. 17
B. 16
C. 15
D. 14
E. 13

Guys - as the OA is not provided can someone please help me and explain how to solve this?


Bunuel's bruteforce using odd and even looks promising! I'd also like to add that you could eliminate some answer options using the same approach.
Since 75 is an odd number. The squares must be of the form -
\(Odd^2 + Odd^2 + Odd^2\) OR
\(Even^2 + Even^2 + Odd^2\)

Alternatively -
\(Odd + Odd + Even\) OR \(Even + Even + Odd\). Thus, the sum of these numbers must be ODD. Eliminate answer option B and C.
Breaking 13, 15, and 17 using further bruteforce. We get \(7^2 + 1^2 + 5^2\). 7 + 1 + 5 = 13. Answer Option A

Bunuel - Please correct me I am wrong, but if this is a general question that appears on the exam, we can conclude -
Sum of squares equal to a number?
* If the number is odd --> Correct answer option will be Odd.
* If the number is even --> Correct answer option will be Even
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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 29 Nov 2015, 11:05
Expert's post
Hi All,

This question can be solved with a bit of 'brute force' arithmetic, but the speed with which you solve it will likely depend on how quickly you can write everything down and how you do the work.

We're asked to find the three positive integers, whose squares add up to 75. To start, we should write down the list of possible squares:

1
4
9
16
25
36
49
64

We're limited to these 8 numbers. To work efficiently, we should work from 'greatest to least'..

If we use 64, then the other two numbers have to add up to 11....but there's NO WAY to make that happen (so 64 is NOT one of the numbers we need).

Next, let's try 49... then the other two numbers have to add up to 26....25 and 1 'fit', so the three numbers are 49, 25 and 1 (7, 5 and 1 --> that sum = 13).

Final Answer:
[Reveal] Spoiler:
E


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Re: The number 75 can be written as the sum of the squares of 3 [#permalink]

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New post 29 Nov 2015, 11:14
enigma123 wrote:
The number 75 can be written as the sum of the squares of 3 different positive integers. What is the sum of these 3 integers?
A. 17
B. 16
C. 15
D. 14
E. 13

Guys - as the OA is not provided can someone please help me and explain how to solve this?


1^2 = 1
2^2 = 4
3^2 = 9
4^2 = 16
5^2 = 25
6^2 = 36
7^2 = 49
8^2 = 64


9^2 = 81
10^2 = 100


Quote:
The sum of the squares of 3 different positive integers is 75


Start from 8^2 = 64

75 - 64 = 11 ; we need 2 other squares to add upto 11 - No possibility

Then 7^2 = 49

75 - 49 = 26 ; we need 2 other squares to add upto 26 - Possibile squares are 25 , 1

So, the required numbers are 7 , 5 and 1

Hence the numbers are 1,5,7

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Re: The number 75 can be written as the sum of the squares of 3   [#permalink] 29 Nov 2015, 11:14
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