bases trouble be me lot

Algebra Level 4

In a certain base system 34 in base x is equal to 43 in base y.
What is the minimum value of x + y x + y ?

Note: x and y are positive integers.


The answer is 16.

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2 solutions

Billy Reynolds
Nov 3, 2014

You can easily translate from any base to base ten using the following equation:

d n b n + d n 1 b n 1 + + d 1 b 1 + d 0 b 0 d_n \cdot b^n + d_{n-1} \cdot b^{n-1} + \ldots + d_1 \cdot b^1 + d_0 \cdot b^0

Where b b is the base, d n d_n is the digit in the n n 's place, and n n is the number of digits in the number minus one.

(For example, 1303 in base 3 is 1 3 3 + 3 3 2 + 0 3 1 + 3 3 0 = 57 1 \cdot 3^3 + 3 \cdot 3^2 + 0 \cdot 3^1 + 3 \cdot 3^0 = 57 )

So, if 34 34 in base x x equals 43 43 in base y y , this translates to a very simple linear equation:

3 x + 4 = 4 y + 3 y = 3 x + 1 4 3x + 4 = 4y+3 \Rightarrow y = \frac {3x + 1}{4}

The solutions must be positive integers, but they must also be greater than any digit in the problem (or the number wouldn't even be valid for that base). The first two sets of integer solutions to this equation, ( 1 , 1 ) (1, 1) and ( 5 , 4 ) (5, 4) , do not satisfy this condition. The first valid solution is ( 9 , 7 ) (9, 7) .

So the answer is 9 + 7 = 16 9 + 7 = 16

Calvin Lin Staff
Nov 3, 2014

[This is not a solution.]

@JaiGupta

Please check that you are receiving email from us which lists the clarification/dispute. The disputes to your problem were along the line of

"There are many answers possible. 16 is the minimum."

I've edited this problem for clarity. Can you review it to ensure I kept the original meaning?

Calvin Lin Staff - 6 years, 7 months ago

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Ya Calvin answer is 16 but I 'll edit it Check now

Jai Gupta - 6 years, 7 months ago

yes, for x+y, from the equation y=(3x+1/4) x+y = x +3x+(1/4) = (7x+1)/4

so is it like maximum value of (7x+1)/4 ??? though it has multiple solutions??

Saikrishna Jampuram - 6 years, 7 months ago

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Note that you are (now) asked for the minimum value of x + y x+y , so there is a unique solution.

See Billy's solution for a detailed explanation of what conditions you are missing, and how to continue.

Calvin Lin Staff - 6 years, 7 months ago

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