Hello there. To solve this question, we'll have to analyze how many weeks there are in a year and determine if Clare will have to work 13 saturdays in a year.
For this, remember that some months have 5 weeks, in some sense, if we consider all the days of a week. But if we only consider a week if there is 7 days, then a month have 4 weeks.
A calendar year consists of 52 weeks (sometimes 53), but since Clare have to work 1 saturday every 4 months, we take the ratio:
![(52)/(4)=13](https://img.qammunity.org/2023/formulas/mathematics/college/ic10bcri4w1vm11htikutzmidgu0cp3i0g.png)
Therefore Clare is right and she will have to work 13 saturdays in a year.
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If Rose have 4.5kg of joint beef, then we convert to grams to find how many portions of 500g there are.
4.5 * 1000 = 4500g
Now, divide it by 500g
![(4500)/(500)=9\text{ portions}](https://img.qammunity.org/2023/formulas/mathematics/college/njuc8qiytol477c218sllhmtshmg2c5n3r.png)
Therefore we multiply this number by 20 to find how many time she'll have to cook this piece of meat
![9\cdot20=180](https://img.qammunity.org/2023/formulas/mathematics/college/bwuhhgsrp96ca8wnuog5k0rwbyakg2obib.png)
And we add 15 that is the time she have to wait for serving, thus
![195\min](https://img.qammunity.org/2023/formulas/mathematics/college/93dh3zd7eqauhjh9xjlae6dc7hspyz6puw.png)
In hours, we get
![3\text{ hours, 15 minutes}](https://img.qammunity.org/2023/formulas/mathematics/college/7ka7kvqqbvzk8ymzuzxr8ye4wtgxyyvkqs.png)
If she want to serve it at 2 pm, the latest time she can start cooking the beef is:
10:45 AM