If we have 48 legs and 20 humps in our herd of camels and dromedaries,
How many dromedaries are in the group?
If we divide the number of legs by 4 we get the total number of animals that are 12.
Now we distribute a hump for each animal and we see that there are 8 left over that correspond to the camels that have 2 humps each. Therefore we have 12 - 8 = 4 dromedaries.