Question

1. how many independent variables should a controlled experiment have?

graphing and data analysis
a clam farmer has been keeping records concerning the water temperature and the number of clams developing from fertilized eggs. the data is recorded below:

water temperature in $^circ$c	number of developing clams
20	90
25	120
30	140
35	75
40	40
45	15
50	0

1. what is the dependent variable?
2. what is the independent variable?
3. what is the optimal water temperature for developing clams?
4. how does the data trend after 30 degrees celsius?

Explanation:

1. In a controlled experiment, there should be only one independent variable to ensure that the effect on the dependent variable can be clearly attributed.
2. The dependent variable is what is being measured or observed. In this case, it is the number of developing clams as it depends on the water temperature.
3. The independent variable is what is being changed or manipulated. Here, it is the water temperature.
4. The optimal water temperature is the one where the number of developing clams is the highest. Looking at the data, at 30°C, the number of developing clams is 140, which is the maximum.
5. After 30 degrees Celsius, as the temperature increases (from 35°C to 50°C), the number of developing clams decreases.

Answer:

1. One
2. Number of developing clams
3. Water temperature
4. 30°C
5. The number of developing clams decreases as the temperature increases.