Slicing Using Factorizing

Algebra Level 2

For positive integers x , y x,y where:

x y = 100 xy=100

and x x is not divisible by 2 2 .

Find the sum of all solutions. If the solutions you obtain for example, (x,y) = (1,2) and (3,4) then your answer will be 1 + 2 + 3 + 4 = 10 1+2+3+4 = \boxed{10} .


The answer is 155.

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1 solution

Mohammad Al Ali
Nov 23, 2014

Given by the question,

x y = 100 = 1 0 2 = ( 2 × 5 ) 2 = 2 2 × 5 2 xy=100 = 10^{2} = (2 \times 5)^{2} = 2^{2} \times 5^{2}

Since x x isn't divisible by 2 2 , the only possible solutions for x x are either 5 0 5^{0} , 5 1 5^{1} or 5 2 5^{2} .

Firstly, case where x = 5 0 = 1 x = 5^{0} = 1 attains us with y = 100 1 = 100 y =\frac{100}{1} = 100 .

Secondly, case where x = 5 1 x = 5^{1} attains us with y = 100 5 = 20 y =\frac{100}{5} = 20 .

The last case, where x = 5 2 x=5^{2} returns us with y = 100 25 = 4 y = \frac{100}{25} = 4 .

Finally, our solutions are ( x , y ) (x,y) : ( 1 , 100 ) (1,100) , ( 5 , 20 ) (5,20) and ( 25 , 4 ) (25,4) .

Hence our answer is: 1 + 100 + 5 + 20 + 25 + 4 = 155 1+100+5+20+25+4 = \boxed{155} .

Is ( 1 , 100 ) (1,100) is a possible solution ?

sujoy roy - 6 years, 6 months ago

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That's totally correct Sujoy, thanks for pointing that out. I must've forgotten to add that to the question somewhere. Updated the question + solution.

Mohammad Al Ali - 6 years, 6 months ago

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you have not updated the solution !!!! The answer is still displayed as 54

Mehul Arora - 6 years, 6 months ago

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@Mehul Arora I have just updated the answer. It takes us 1-2 days to review through the requests, and would take longer over the weekend.

Calvin Lin Staff - 6 years, 6 months ago

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