This question follows and requires information from the previous questions.

Answering question 3a(iii) you found that percentage of male calves retained after three months:

P (male retained)=0.55 * 0.3 * 0.2=0.033

0.55 males caves were born, 0.3 retained after the first months and out of these 0.2 retained after the third months. (*Say, out of thousand calves born you would have retained 33 males*)

We know that male to female ratio is to be changed to 1:10 thus we should have 10 times more female than male calves retained:

P(females retained) = 0.033 * 10 = 0.33

(*Out of thousand calves born you would have 33 male and 330 female calves retained*)

We know that originally we had 0.45 female calves (*out of thousand calves born 450 were female*), therefore

P(females sold) = 0.45 - 0.33 = 0.12

(*out thousand calves that would be 450 - 330 = 120*)

We were asked to find proportion of female calves being sold. We know that 0.12 calves out of 0.45 were sold, thus:

0.12/0.45 = 0.267 or 26.7%

(*or 120 female calves out 450 that were born*)

I hope that helps. Please ask if you need more clarification.