S1 Question from CIE Pastpapers

So this question has been bothering me for a while and i have asked a few of my teachers and they told me how to solve it too but i forgot because it was like 2-3 months back when i asked them about it so im asking you guys to please tell me how this question will be solved. The question is from June 2003 paper Question number 6.

6 The people living in 3 houses are classified as children (C), parents (P) or grandparents (G). The numbers living in each house are shown in the table below.
House number 1: 4C, 1P, 2G
House number 2: 2C, 2P, 3G
House number 3:1C, 1G

(i) All the people in all 3 houses meet for a party. One person at the party is chosen at random. Calculate the probability of choosing a grandparent. [2]

(ii) A house is chosen at random. Then a person in that house is chosen at random. Using a tree diagram, or otherwise, calculate the probability that the person chosen is a grandparent. [3]

(iii) Given that the person chosen by the method in part (ii) is a grandparent, calculate the probability that there is also a parent living in the house. [4]

I have solved the first 2 parts but am facing problems in the last part. The answers are:

i. : 6/16
ii. : 17/42
iii. :10/17

Someone please explain the 3rd part to me i have the paper on wednesday.

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S1 Question from CIE Pastpapers

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