Question

In an experiment to find out whether sugar dissolves faster in hot water than in cold water, what should be measured?

Rohan wants to test: Does the type of surface affect how far a toy car rolls down a ramp? Which of these should he not keep the same?

Sameer wants to show that a fertiliser makes plants grow taller. He adds fertiliser to plant P kept on a sunny window and no fertiliser to plant Q kept in a dark corner. Plant P grows taller. What is the main problem with his conclusion?

Assertion (A): In a fair test, only one variable is changed at a time. Reason (R): If several variables are changed together, we cannot tell which one caused the result.