Chicken-Egg-Days Problem

7 Chicken lays 8 eggs in 64 days. If we need 27 eggs in 42 days how many chickens we need?

MetroEye: This problem is similar to work-person-rate problem.

i.e; W1/(M1*H1) = W2/(M2*H2)
where W is work to be done,  M is the number of persons required, Hour is time required. 

Applying the above equation 
8/(7*64) = N/(27*42) where N is the number of chickens needed.

Solving N = 36

36 Chickens are needed to get 27 eggs in 42 days.