Rate ValueEdit
Every dificulty has 1 slot unlocked on default (1:1:1). In order to unlock the others you will need a specific ammount of rate value. This value is in fact the current earning of your two Dragons:
Earning Formule  Unlock Requirement 



If your rating is below the 50 only 1 slot from every dificulty is open. What makes every dificulty an 33.33% chance. 
Calculate Earning RateEdit
What is base gold/ increase gold?
Every dragon has a base gold (gold/minute at level 1) and the increase value (added for each level after). You can find these numbers on the dragon page by either ways:
 In the infobox, notice at this Generation: and take the numbers in the bracet. There are usually 3 numbers in the bracet, and the display should be (base gold/ increase  difficult group)
 Clicking to show the Earning Tab: Then read the first line to look for the numbers base+increase
Calculate Earning RateEdit
 If the level is smaller or equal to 10: Rate = Base + Increase * (level  1)
 If the level is greater than 10: Rate = Base + Increase * 9 + 0.5 * Increase * (level  10)
 The Total Rate is sum both rates of the 2 parents: Total Rate = Rate (parent A) + Rate (parent B) This value is used to assess how much slots open for each difficult group
 For example: Blizzard Dragon has 6/4 earning rate. A level 9 Blizzard Dragon has rate = 6 + 4 * (9 1) = 38. A level 15 Blizzard Dragon has rate = 6 + 4 * 9 + 2 * (15  10) = 52
Slots UnlockEdit
Let's rewrite the 3 arrays of Difficult 1, 2, 3 into this for easy to look up & count
Slots open  Difficulty 1  Difficulty 2  Difficulty 3 
1  0  0  0 
2  50  50  100 
3  55  70  200 
4  60  90  300 
5  65  110  400 
6  70  130  500 
7  75  150  600 
8  80  170  700 
9  85  190  800 
10  90  210  900 
11  95  230  1000 
Once you have the Total Rate, use that number to compare to this table to get the number of slots unlocked for each difficulty group. To count the number of slots unlocked:
 Look at the column "Difficulty 1", find the largest number which <= Total Rate
 Match that row to the column "Slot open": number of slots unlocked for Difficulty 1
Repeat these steps for the Difficulty 2, as well as Difficulty 3. Now you have 3 numbers A, B, C. The chance of each group will be the number of slots unlock (A or B or C) divide sum (A + B + C).
 For Ex: Total Rate is 203 open [11:9:3]
 Difficulty 1: largest number <= 203 is 95
 Slot open for Difficulty 1 is A = 11
 Difficulty 2: largest number <= 203 is 190
 Slot open for Difficulty 2 is B = 9
 Difficulty 3: largest number <= 203 is 200
 Slot open for Difficulty 3 is C = 3
 Chance of group Difficulty 1 is A/(A+B+C) = 11/(11+9+3) = 47.83%
 Chance of group Difficulty 2 is B/(A+B+C) = 9/(11+9+3) = 39.13%
 Chance of group Difficulty 3 is C/(A+B+C) = 2/(11+9+3) = 13.04%
FactsEdit
The percent chance of each difficulty group depends on the rate value. (See the chart below)
 For Difficulty 1: Highest rate is 69.23% when rate value is 85  89 (recommended). Secondly highest is 68.75% when rate value is 95  99
 For Difficulty 2: Highest rate is 44.00% when rate value is 230  299 (recommended for high level player). Secondly highest is 40.00% when rate value is 50  54 (recommended for new player)
 For Difficulty 3: Highest rate is 33.33% when rate value is 0  49 or 1000+