Four plants receive (50,mL), (100,mL), (150,mL) and (200,mL) of water respectively. How many levels of the independent variable are present?

Correct answer: Four

The direct answer is C: four levels. A level means one distinct value or condition of the independent variable. The independent variable is the amount of water given to the plants. The listed values are 50 mL, 100 mL, 150 mL and 200 mL. These are four different values, so there are four levels. Option A, two, counts too few values. Option B, three, misses one of the four amounts. Option C is correct because every distinct water amount counts once. Option D, five, adds a value that was never used. Do not count the plants only; count the different settings of the variable. Even if several plants received the same amount, that would still be one level, but here each listed amount is different. Memory cue: number of levels equals number of distinct values tested.