genetics probability question

[I GET BUCKETS]

can someone please explain why this is the answer? Also, these genetics probability problems always get me when doing practice questions, any tips on how to solve them in general?

 

[humblethinker]

because you need the Xi from the female to pair with the male Y, you need to only consider the percent chance of getting Xi from females that can donate it. So 100% of the 15% XiXi will donate an Xi so by multiplying that equals 0.15. 50% of the 50% XiXs will donate an Xi so by multiplying that equals 0.25. 0% of the 35% XsXs will donate an Xi so by multiplying that equals 0. Sum up all probabilities by doing 0.15+0.25+0 and you get 0.40 = 40%. I would save genetics problems for the end of your section as sometimes the calculations under time constraints can appear much more difficult than they really are.