Which margins can be increased for short letters?

μ=  17.42

var=  12.891= 12.9

σ = 3.59

Explanation:

As the number of trials are fixed  i.e 67 and the success is also fixed i.e 26% or 0.26 this is treated as a binomial experiment.

The mean of the binomial experiment is calculated as

μ= np = 67*0.26= 17.42

This is the same as the expected value of number of yellow eggs.

E(y)= np=μ=  67*0.26= 17.42

The variance  of the binomial experiment is calculated as

var= npq  = 67*0.26(1-0.26)= 67*0.26(0.74)= 12.8908= 12.891

The standard deviation  of the binomial experiment is calculated as

σ =√npq= √12.8908= 3.590376  = 3.59038= 3.5904 = 3.590= 3.59