Probability Distributions 2021 NCEA exam walkthrough

There may be errors, I did this as soon as I got the exam :S

[tkdyt]

I am having trouble understanding how Q3 part b) i) works. Why exactly do we need to divide? I know that it is something to do with the conditional probablity

[coollittlebinch]

Hi I was just wondering, how do we know when to use Bcd and Bpd on our graphix calculators?