GUIDE]  Buy Runes, or Combine Runes...?
(Yes, i do realize that by accident i named the title with "Sell Runes" which actually is suppose to be "Combine Runes", sorry for the mistake, but i don't know how to fix it...)
Ok, so we all know about the cool feature League of Legends has to offer with Runes which can give some amazing advantages over enemies IF used properly.. They also decided to provide a Rune combining System to allow user's to Combine runes to produce the same (or better) runes of a random type. Some of us have wondered that massing smaller runes to produce greater ones will have a very positive effect while others (such as me) don't enjoy the random generated rune system and would rather have that nice 100% chance of getting the runes we desire. Listed below are Several Cases which show how in each aspect they can be positive of negative... Some of the least expensive runes in the store right now are worth 15 IP. Ex: Lesser Mark of Strength +0.18 Dmg . If we theoretically bought 5 of the same kind and then combined them together we will then generate a random Tier 2 rune. At the total cost of 15 x 5 = 75 IP WHICH is pretty good. Considering that the normal cost of tier 2 runes is approx ~165 IP BECAUSE we want to know it's EFFECTIVENESS we will use a total of 75 x 2 = 150 IP points to create tier 2 runes. (Which is the near the same value as buying directly from the store a tier 2 rune for 165 IP) Also we can consider the fact that if we produce two random tier 2 runes we can combine those two further to obtain another random tier 2 rune. So in the end, using 150 IP you have 3 chances of getting a Specific tier 2 Rune using collectivly tier 1 Runes with a value of 15 IP. OR you can use 165 IP to have a 100% Chance to obtain a tier 2 Rune for 165 IP. The total possibilities of getting a rune are dependent on how many different types of runes there are and what you want. The different Runes are HP Reg Hp Mana Mana Reg Armor Magic Resistance Damage Ability Power Armor Penetration Magic Penetration Dodge Rate Critical Strike Rate Crititcal Strike Damage Ability Cooldown Which gives us a total of 14 different possibilities... Because we have 3 chances of getting a specific rune of tier 2 from the possibilities of 14 different kinds, that leaves us with a ~21.4% chance to get the specific rune we wanted. Tier 2: 21.4% Chance to get a specific tier 2 Rune you desire for 150 OR 100% Chance to get a specific tier 2 Rune you desire for ~165 IP kinda more reliable to just buy the Rune from the shop eh? NOW, lets use Tier 3 Runes. If we did this 5 times, and tried to get a tier 3 Rune we would use 375 IP to get a randomly generated rune of Tier 3. The least expensive tier 3 runes are 205 Ip, and the most expensive are around 2050. Each batch of tier 1 runes of 15 Ip (each batch costing us 15 x 5 x 5 = 375) would produce randomly a Tier 3 Rune. If we decided to compare this cost with that of 2050 IP then a little bit more math is going to be involved.... The closest numbers 2050 can be divided by 375 are 5 and 6. 5 x 375 = 1875 6 x 375 = 2250 Using 1875 Ip we could theoretically create 5 Random Tier 3 Runes, which could create another 2 extra Tier 3 Runes (with one remaining) which could create and extra 1 tier, which can then combine finally with the last remaining tier 3 Rune, giving us a total of 9 chances to obtain a specific Tier 3 Rune. Using 2250 Ip we could theoretically make 6 Random Tier 3 Runes which could create another 3 extra Tier 3 Runes, which could create an extra tier 3 Rune (with one remaining) allowing that one to combine with the last remaining tier 3 Runes to give a total of 11 Chances to obtain a specific Rune we desire for 2250 IP (I hope im not confusing you too much!) The probabilities of each one will then be... Tier 3 Runes: 64.3% Chance to obtain a specific Tier 3 for 1875 IP OR 78.6% Chance to obtain a specific Tier 3 Rune for 2250 IP OR 100% Chance to obtain a specific Tier 3 Rune (from the store) for 2052050 IP So in the end, it doesn't seem like Rune combining is even that great...HOWEVER, please realize that there are certain "special" runes which can only be obtained from the Rune combining system. So it isn't "completely" useless... Also, note that most people don't mass one specific type of rune, some people might chose from 3 specific Rune such as, Critical Strike, Critical Damage and Attack Speed (mostly because there are caps on these values to stop you from becoming Chuck Norris) so the randomizing does help allow you to become more powerful in different area's. Also note that I did NOT specify anything on the Rune colors. I decided to keep this variable out of place because it would complicate things further. For my suggestions here is what i recommend. Use Rune Combining only for Tier 3 Runes. (and if it exists Tier 4 Runes , possible they might make an update on this..) If you filling up one of the last spots in your Rune Book I STRONGLY suggest that you do not use the Rune combining system I hope you enjoyed this guide everyone! Thanks for reading it! P.s. Please tell me if i had made any mathematical errors and i will correct them A.S.A.P. 
How did you calculate your chance to obtain a specific Tear 3 rune? It seems like those probabilities are a bit high.
There are 87 possible runes at Tier 3 that are available. So when you do a 6 Tier 2 rune combination you have a 1/87 chance to get a specific rune. Taking your 2250 IP example, you have 6 chances or an addative probability of (1/87)*6 = .0689 or a 6.9% chance to get a specific rune. If you didn't get the rune you wanted in that case, you would then have a 1/85 chance at a 2nd combination (theoretically if you can't reduplicate the same runes you put in) for your last 5 combinations giving you (1/85)*5 = .0588 or 5.9% chance to get a specific rune. So your total overall probability of obtaining one specific rune is 12.8% There's also the possibility that you're looking for multiple runes which changes your probabilities a bit, but that's variable between individuals. On the value side, there's also serious consideration for the probabilities of getting the different types/values of Tier 3 Runes. As you pointed out, an 1800 IP cost range for Tier 3's can cause some pretty significant valuation changes depending on what you land. 
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wut happens when u combine tier 3 runes?

And wut about the limited edition christmas runes?

Hmm... I would think the most useful aspect of the cominber is the fact that you can buy tier 2 runes, use them for a while/test out a champion, then trade them in for tier 3 runes once you're a bit more advanced.

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Ex: Critical Chance Red Rune: 1% Blue Rune: 1.5% Yellow Rune. 1.32% Purple Rune: 3.24% Now EACH batch to make a tier 3 Rune Costs 375 IP 5 of Tier 1 (15 IP) = 1 Tier 2 Rune for 75 IP 5 Tier 2 Rune for 75IP = 1 Tier 3 Rune for >375 IP< So for 2250 Ip you can have a total of >6< TIER 3 RUNE. In the end you get 11 Chances to produce a tier 3 Rune of a specific BONUS TYPE (im sorry if i did not specify this before) 
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For example...when i combined a few runes the other day i got a Purple Rune that gave an addadtive bonus which at level 18 gave 3.94 Hp Regen per 5 seconds. When i tried looking for this Runes (at tier 2, a purple rune) in the store, it was unavailable... The only one i found gave only 2.1 Hp Reg per 5 seconds... See my point? 
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