The chance of a successful fusion was changed just before Thanksgiving 2013. The table below, gives the new percentages that determine how the chance of a successful fusion depends on the levels of the two dinos being fused.
Chance or probability function for one dino
Comparision: You can see some of the chances are better and some are worse. Chances for toddler dinos are slightly worse than before. But the chance associated to one adult has been increased form 75% to 80%. So, now it pays even more than before to fuse teen or adult dinos only.
Details: These probabiities are the same whether the dinos are from two different biomes or the same biome. For those who are looking inside the DinoFusionClient file, successPercentAA refers to dinos from the same biome A. And successPercentAB refers to dinos from two different biomes A and B. Fortunately the chances are the same in both cases, so we need not worry about this distinction for now.
Chance or probability function for two dinos
The chance of a successful fusion, depends on both dinosaurs that you fuse, and is simply the average of the chance for each.
Chance = (p1 + p2) / 2
Before, all chances were odd, so the sum was always even. But now we have the even number 80% for adult dinos. So be careful.
i. The chance of a successful fusion if you fuse a level 7 teen and a level 9 teen is:
Chance = (p1 + p2) / 2 = (53 + 57) / 2 = 55%
ii. The chance of a successful fusion if you fuse two level 10 adults is:
Chance = (p1 + p2) / 2 = (80 + 80) / 2 = 80%
iii. The chance of a successful fusion if you fuse two level 4 toddlers is:
Chance = (p1 + p2) / 2 = (25 + 25) / 2 = 25%
So, the chance with two level 4 toddlers is now only 1 in 4. Before, it was 1 in 3, which was much better.
Fusion Guarantee CalculationsEdit
You also have the option to guarantee fusion for a nominal crystal tax. Note that a guarantee of fusion just means your chance of getting a dino is increased to 100%. It does not mean you will get the dino that you want. The number of crystals needed to guarantee fusion is a base fee of 10 crystals + 1 crystal for each percentage point needed to boost the fusion chance up to 100%.
Here is the formula for the fusion guarantee fee.
Fusion Boost Fee = 110 - (p1 + p2 ) / 2
i. To guarantee fusion of a level 9 teen and a level 10 adult, the crystal fee is:
110 - (p1 + p2) / 2 = 110 - (80 + 57) / 2 = 42 Crystals
Note: The result as a floating point is actually 41.5, so round up to get the actual fee of 42.
ii. To guarantee fusion of two level 10 adults, the crystal fee is:
110 - (p1 + p2) / 2 = 110 - (80 + 80) / 2 = 30 Crystals
This last calculation agrees with the following screenshot confirming the required Guarantee Fusion charge is indeed 30 crystals for two adult dinos.