But let’s say old/adult 48 male to 40 female and

young/not old 7 male to 5 female

so total 55 male to 45 females

and let’s say internal ratios are same, in both west lake and east lake, for convenience means old male to old female ratio 48to40 =1.2:1

And young male to young female 7to5=1.4:1 so we can apply these ratios to east lake

So we have assumed same internal ratios for both lake that is for every 48 male old ducks 7 young male duck and 40:5 for old females to young females

Now we get 48+7=65 bez internal ratios are same so by solving all equations like that we get _56.72 old male to 20 old female and

47.27 young male to 14 young female (( ratios are not quite adding up for significant and less proportion of many more male old compared to less more young male for comparative females but some math guy can get ratios for that in infinite series of numbers)

So now you can see we can infer answer A but with same perspective we can also infer B. thank you Diana for posting my query. Sage tell me where am I going wrong here dastinpixel also suggesting nearly same thing.

And we don’t know actual numbers that is why I assumed internal ratios are same.

yes, this is an invalid argument.