Mia gives four bean plants different amounts of fertilizer: 0 g, 2 g, 4 g, and 6 g. She measures each plant's height after three weeks. What is the independent variable in her investigation?

A class rolls the same toy car down a ramp set at 10, 20, and 30 degrees, then measures how far the car travels past the ramp. What is the dependent variable?

Ben tests whether salt changes how fast water freezes. He puts 100 mL of water in each of four identical cups, adds a different mass of salt to each, and places them all in the same freezer. What is a controlled variable?

A group tests a new plant food on tomato seedlings. Every seedling gets the same soil, light, and water. What should the control group receive?

A student wants to know whether a cloth sleeve keeps hot cocoa warm longer. Two cups start at 80 degrees Celsius. Which plan is a fair test?

A team measures how long a paper airplane stays in the air: Trial 1: 3.2 s, Trial 2: 3.0 s, Trial 3: 3.4 s, Trial 4: 3.1 s, Trial 5: 3.3 s. Why did they run five trials and take the mean?

Four groups time how long an ice cube takes to melt: 210 s, 205 s, 215 s, and 95 s. The fourth group left their ice cube on a sunny windowsill. What best explains the odd result?

A town's records show that in months when ice-cream sales rise, the number of sunburns also rises. What conclusion do these data support?

While observing pond water with a hand lens, a student writes: 'The water is cloudy and smells musty.' How should this observation be classified?

A team must measure the volume of an irregular rock to the nearest milliliter for their data table. Which tool should they choose?

In an experimental investigation, the independent variable is the one factor the investigator purposely changes.

A student asks, 'Does the color of a container affect how quickly water inside it warms in sunlight?' Why is this an investigable question?

A class records the temperature of a cooling cup of water every two minutes for 20 minutes. Which graph best displays how the temperature changed over that time?

Before testing, a team writes: 'If we add more salt to water, then the water will boil at a higher temperature.' What is this statement?

A group is about to pour a warm liquid from a beaker into a graduated cylinder. What safety procedure should they follow first?

Two groups test how sunlight affects grass growth. Group A puts one tray in sun and one in shade with the same soil and water. Group B changes the soil and the light together. Whose plan gives clearer evidence?

A student records the number of birds visiting a feeder each morning for a month without changing anything about the feeder. What kind of investigation is this?

A team measures the mass of a mineral sample three times: 24.0 g, 25.0 g, and 26.0 g. What is the mean mass they should record in their data table?

A student claims a new insulating sleeve keeps drinks hot longer. She has a photo of a steamy sleeved cup, ten classmates' opinions, the maker's advertisement, and a timed test of two identical cups. Which evidence best supports the claim?

A school compares two reports on local river quality. One is a company's webpage saying its plant is 'completely safe', the other lists monthly oxygen and temperature measurements from a university lab. Which is the more credible source?