## Euclid 2023 Question 4, CEMC UWaterloo

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#### Difficulty: 6

#### This problem is tagged with euclid, euclid23, highschool.

**(Euclid 2023, Question 4, CEMC - UWaterloo)**

(a) Liang and Edmundo paint at different but constant rates. Liang can paint a room in $3$ hours if she works alone. Edmundo can paint the same room in $4$ hours if he works alone. Liang works alone for $2$ hours and then stops. Edmundo finishes painting the room. How many minutes will Edmundo need to finish painting the room?

(b) On January $1$, $2021$, an investment had a value of $\$400$.

From January $1$, $2021$ to January $1$, $2022$, the value of the investment increased by $A\%$ from its value on January $1$, $2021$ for some $A > 0$.

From January $1$, $2022$ to January $1$, $2023$, the value of the investment decreased by $A\%$ from its value on January $1$, $2022$.

On January $1$, $2023$, the value of the investment was $\$391$.

Determine all possible values of $A$.

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