Can someone please help me solve a hatchery sexing disclaimer problem?

[stephs]

I'm struggling to wrap my head around this problem!

If McMurray hatchery says that there is a 90% accuracy rate for an all-pullet delivery, and I ordered 25 chicks, then what is the chance that one of those 25 chicks may be a rooster??
I recall getting an A in statistics, but no matter how long ago that class was (indeed it was) I seem to have let the real knowledge fly the coop.

Thanks! I surrender my A to the person who can solve the problem first

 

[bluey]

90 percent accuracy suggests 10% inaccuracy.

10% of 25 is 2.5 roosters.

 

[Becky_H]

90% means that up to 10 out of a 100 chicks could be roos. Breaking that down it's 1 in 10 could be a roo. So if you order 25, that's 2 and a half times the 1 in 10, so. You could get 2.5 roos and still have 90% girls.

 

[fiftyfifty]

Oh this is a fun one! But I need to clarify what you are asking exactly. Are you asking:

"If I get 25 chicks, what is the chance that one, and only one, chick is a rooster?"

or are you asking:
"If I get 25 chicks, what is the chance that at least one chick is a rooster?"

I think the answer to the second question is 93%. I got that by multiplying 0.9 x 0.9 x 0.9.....x 0.9 etc. 25 times. That gives me 0.072. This is the fraction of buyers who would get no roosters. I multiply this by 100 to give me the percentage of buyers who would get no roosters. This is 7.2%. So 100%-7.2% is about 93% who would not get no roosters (i.e would get at least one rooster). I hope someone will check my math on this.

The first question is harder for me to answer. It's basically asking the same question as "If you have 2 kids, what are the chances one will be a boy and one will be a girl?" (the answer is 50%)....or "If you have 3 kids, what are the chances 2 will be girls and one will be a boy" (the answer is 37.5). But instead with the chance of any individual being a female at 90% rather than 50%, and with a family of 25! I could do it by hand but it would take me all day. I'm sure there is a formula somewhere.

Of course all this rests on the assumption that the sexers' accuracy rates are exactly 90%, when in actuality the hatcheries just guarentee it won't be worse than 90%. I bet it varies person to person and breed to breed.

I hope someone smarter than me will chime in.

 

[DiVon80]

My opinion-I think they are really accurate in the sexing of the large fowl and just say the possibility of 10% is just to cover them in case a roo gets threw. I got 26 babies from Ideal. I ordered 24 poulets and 2 roos=got just what I ordered. Was even hoping one of the Buff O's would of been a roo. BUT all girls. Just to make a long story short IF you want a roo order one, chances are if you order all girls you will get just that.

 

[enola]

2.5 roosters ?

I wonder what .5 of a rooster looks like !

Will it be the front half, the back half or one or the other side ?

 

[Isabella]

Out of my 8 Ameraucana pullets I ordered I got 4 roosters. So they only got it 50% right. The rest of the order of other chick breeds were correct. It was just the Ameraucanas they messed up on.

 

[MoodyChicken]

Quote:
That means you'll get two roosters and a hermaphrodite, or just a set of masculine legs running around.

 

[saddina]

The more pressing issue is if you'll get sent straight run anyway (I ordered all hens and 50% have been roos).

 

[greathorse]

I am guessing a little bit here, but I think there is a possibilty the Ameraucana are vent sexed and many other varieties are wing feather sexed.. I think wing feather sexing is very close to 100% I think just the speed at which they work they can sometimes throw one the wrong way.

I dont know that for sure, but I know most breeds are linked so they can sex by looking at the wing feather.