Static electricity investigation

This task is about critiqing the method used in an investigation.

Sandra did an experiment with static electricity. She ran a comb through her hair ten times and then held it over a pile of small pieces of paper.
She counted the number of pieces the comb picked up. She repeated the experiment three times.
Her results were:
 
Trial Number of pieces of paper picked up
1 3
2 7
3 5
 

Question

a)  She noticed her results varied quite a bit.
    To make her experiment as fair as possible what is the best thing for her to do next?

    • Take another reading and see which of the three trials it is nearest.

    • Repeat the experiment with another comb.

    • Choose the highest reading.

    • Do the experiment several more times and average the readings.

    • Calculate the average of the three readings.

Question

b)  Which of the following factors is most likely to increase the fairness of Sandra's test?

    • Possible changes in atmospheric conditions

    • Static electricity building up throughout the experiment

    • Sandra's decision to comb her hair a set number of times before each trial

    • Changing the distance Sandra held the comb above the paper

    •  Varying the shape of the pile of paper