Number of chickens that had metal rings = 50
The next day, number of chickens that had metal rings = 6
Probability = 6/50
This probability must be used to find the total number of chickens.
The farmer must keep rounding the chickens up until one day, all 50 of the chickens rounded up have metal rings on them.
So the numerator will become 50 whilst the denominator will be the total number of chickens.
Let total number of chickens = C
6/50 = 50/C
C = (50 x 50)/6 = 2500/6 = 416.66666 ≈ 417 chickens