Can you find a + b + c a+b+c ???

Algebra Level 2

Find a + b + c a+b+c . If a a , b b and c c is a positive integer a + 1 b + 1 c = 1.5 a + \frac{1}{b + \frac{1}{c}} = 1.5


The answer is 3.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

4 solutions

This is simple if we can express 1.5 = 3 2 1.5=\frac{3}{2} in the form of a continued fraction: 3 2 = 1 + 1 2 = 1 + 1 1 + 1 1 a = b = c = 1 a + b + c = 1 + 1 + 1 = 3 \frac{3}{2}=1+\frac{1}{2}=1+\cfrac{1}{1+\frac{1}{1}}\rightarrow a=b=c=1\rightarrow a+b+c=1+1+1=\boxed{3}

If you don't know much about continued fractions,read the Wikipedia article on it.

nice solution :D

Paul Ryan Longhas - 6 years, 3 months ago
Marco Luca Sbodio
Feb 22, 2015

Here is how I solved it:

a + 1 b + 1 c = a + 1 b c + 1 c = a + c b c + 1 = a b c + a + c b c + 1 = 3 2 a + \frac{1}{b + \frac{1}{c}} = a + \frac{1}{\frac{bc+1}{c}} = a + \frac{c}{bc+1} = \frac{abc + a + c}{bc + 1} = \frac{3}{2}

where the last equality is given by the problem statement.

Now we can say b c + 1 = 2 b c = 1 bc + 1 = 2 \Rightarrow bc = 1 and since a , b , c a, b, c are positive integers we have b = 1 , c = 1 b = 1, c =1 .

Similarly we can say a b c + a + c = 3 abc + a + c = 3 , and since b = 1 , c = 1 b = 1, c = 1 we have 2 a + 1 = 3 a = 1 2a + 1 = 3 \Rightarrow a = 1

Therefore a + b + c = 1 + 1 + 1 = 3 a + b + c = 1 + 1 + 1 = 3

Good job :D

Paul Ryan Longhas - 6 years, 3 months ago
Paul Ryan Longhas
Feb 21, 2015

Note that a = 1 a=1

1 b + 1 c = 1 2 \frac{1}{b+ \frac{1}{c}} = \frac{1}{2} b + 1 c = 2 \ b + \frac{1}{c} = 2 = > b = c = 1 => b = c = 1 Thus, a + b + c = 1 + 1 + 1 = 3 a+b+c = 1+1+1 = 3

Scott Ripperda
Mar 24, 2015

There is a grammar error in the problem as stated. It should read:

Find a+b+c. If a, b, and c are positive integers.

Otherwise you could technically assume that a and b are not restricted to positive integers which would give you an infinite number of solutions.

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...