In the equation $\frac{1}{j} + \frac{1}{k} = \frac{1}{30}$, both $j$ and $k$ are positive integers. What is the sum of all possible values for $k$?
This problem is WAY more involved than you may think!!
1/j + 1/k = 1/30
Let 30 = z
j and k must be > 30
So
Let j = z + m and k = z + n
So we have
1/ ( z + m) + 1/ ( z + n) = 1/z
(z +n + z + m) 1
____________ = ____ cross-multiply
(z + m) (z + n) z
(m + n + 2z) z = (z + m) (z + n)
2z^2 + zm + zn = z^2 + zm + zn + mn
z^2 = mn
30^2 = mn
900 = mn
Now....I WILL NOT list all the integer possibilities for this problem but here's a start
mn = 900
So we have that
m n j = z + m k = z + n
1 900 31 930
2 450 32 480
3 300 33 330
4 225 34 255
.
.
.
And so on !!!!!
WolframAlpha has done the heavy lifting here :
https://www.wolframalpha.com/input?i=1%2Fj+%2B+1%2Fk+%3D+1%2F30
P.S. - I wouldn't even attempt to sum all the positive k"s