I’m bad at math but not so bad at logic. How about this…
39+91>>>100+60
(Well…it makes sense to me. If it’s not right, how about you try to figure out MY answer!!) :s 
Here’s my attempt…
The pattern is (look at the sum and product of each side) : -
A + B -> X + Y
where X + Y = A + B + 10
and A * B = X * Y
Check this…
1’st line
10 * 21 = 6 * 35 = 210
10 + 21 = 31 -> 5 + 35 = 41 (31 + 10)
2’nd line
21 * 34 = 51 * 14 = 714
21 + 35 = 55 -> 51 + 14 = 65 (55 + 10)
So,
39 + 91 -> X + Y
where X + Y = 130 + 10 = 140
and X * Y = 39 * 91 = 3549
This yields a very ugly quadratic equation with even uglier roots…
X^2 - 140X + 3549 = 0
This doesn’t give a very pretty solution though =>
39 + 91 -> 106.7559519 + 33.2440481 
So, perhaps my assumptions were wrong… :s
Definitely something to do with factors:
10=25
21=37
Therefore solution = (23) = 6 and (57) = 35
21=37
34=217
Therefore solution = (317) = 51 and (72) = 14
39=313
91=713
The only thing is, I don’t know which order to multiply in. So solution could be:
(21,169) or (39,91) [identical]
Unless someone can work out how they picked the ordering.
[quote=“daasgrrl”]Definitely something to do with factors:
10=25
21=37
Therefore solution = (23) = 6 and (57) = 35
21=37
34=217
Therefore solution = (317) = 51 and (72) = 14
39=313
91=713
The only thing is, I don’t know which order to multiply in. So solution could be:
(21,169) or (39,91) [identical]
Unless someone can work out how they picked the ordering.[/quote]
:bravo: :bravo: :bravo: 
:bravo: :bravo: :bravo:
Daasgrrl, well done! I managed to check the solution on the site the puzzle came from, it needs some translation but the numbers are there …
[quote]Okee, hier de oplossing: als we de eerste regel bekijken, zien we dat de getallen 10 en 21 maar op
:bravo: Well done ! Also true for reading Dutch text to verify solution.
I made the answer ‘blue with yellow stripes’. :s
Heh - thanks for the confirmation (I was aware that one could probably trace back the URL, but I didn’t try it). Although it wouldn’t pass as a true logic puzzle IMO unless there was some designated pattern for choosing which factors to multiply…OK, I’m a geek :help: