Damnit, I should have previewed. Good work, Straun.
Stranger
That’s a very kind thought, but I’ve just ponied up anyway. Let the search-a-thon begin!*
- well I’ll leave it until all the US folk are in bed.
Yay! Welcome! Since you’ve proven yourself worthy, we can do either the goat or the calamari for your initiation – what say you?
No way, that’s four 7s.
Oh wait…
Sturan is the person that sent it to jjimm in the first place.
Or (s)he is really smart.
Actually, it’s not that tough. Try this:
(2)(50) = 100
(2)(49 + 1) = 100
((7+7)/7) (77 + 1) = 100
Now multiply the first set of parentheses by 7 and divide the second set by 7, such that:7((7+7)/7) (1/7)(7*7 + 1) = 100
(7+7) (7 + 1/7) = 100
The trick is not minding that your answer involves a rational fraction that doesn’t reduce to an integer.
Stranger
Ummm, that’s way overthinking compared to my process. Obviously there are two 49s available so only a further two is required. Given a one to play with, a fraction presents itself. Mind you I had to check it with calc. Oh, and if there’s any goat going about, could I have it curried please.
He! And it’s my real name too. Don’t worry about misspelling it, I’ve got used to it. It’s not a totally obscure name in these parts, but it isn’t an everyday one either. Straun, and gulp!!! Strewen are the ones I get most often.
__
77/.77 + 1
(works for any digit)
How does that work?
The bar over the .77 indicates it repeats forever, giving it a value of 7/9.
So
__
xx/.xx = xx/(x/9) = xx*9/x = 11 * 9 = 99
It would work for only 3 7s (or any digit) as well. The OP should send it back to the person he got it from as a return challenge.
Doesn’t your expression just tend towards 100, though? I mean it would always test as being less than 100?
It might be one of those 2+2=5 for large values of 2 things, but I’ll cheerfully admit to not being able grasp much/any number theory stuff. God knows how I managed to get through my degree.
Thinking any mathematical operator was allowed I just instantly assumed 7[sup]2[/sup]+7[sup]2[/sup]+7/7+1
Well, if you’re allowed to use decimal points, there’s a simpler solution:
(77/.77)*1=100
Struan, the whole “Does 0.999… =1” issue has has been addressed by The Perfect Master and rehashed several times on the SDMB (such as here and here). At this point it’s pretty much axiomatic that they’re equal.
[Welcome to the Boards, but don’t even think of asking whether ducks’ quacks echo, where the missing dollars went in hotel transactions, the identity of the three words that end in -gry, or the origin of the phrase “The whole nine yards”.] 
Struan, are you by chance a James Clavell fan?
(I’m currently rereading King Rat.)
I was all ready to jump in with my trick solution but then saw the time of the OP. Oh well, I’ll throw it out there (and then you guys can throw it out.)
7*7+7+7+1=100.
It’s in octal, of course. 
No, Struan is my real-life first name.
Okay…welcome aboard!
A variation on this one:
Imagine the 7s are like in an LCD, with vertical right strokes. After you make the two Ls, take the remaining 7s, and place each one over an L, sliding it down to meet the L on its upper left and lower right. So what you have are two LCD 0s. Place them after the 1.