Joint Variation and Combined Variation - Definitions

$$\text{National Mushroom Day}$$

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Today, October 15th, is National Mushroom Day!

Kristi is trying to make a mushroom pizza. She wants to go out and pick the mushrooms herself. She knows from past years that the number of mushrooms she can fit on her pizzas varies jointly with the time spent searching and the number of tomatoes in her garden.

Last year, Kristi had $2$ hours free to look for mushrooms and her garden had $16$ tomatoes. Her pizzas held $48$ mushrooms.