substituting a different coin flipping the coin twenty more times taping a weight to one side of the coin flipping the coin over a smoother surface
I gave my students this multiple choice question: A student flips a coin four times. It lands "heads" up three times. The student concludes that the coin will land "heads" up three times out of four. What will make the conclusion more accurate?

Only one answer is correct among these 4 choices:
- substituting a different coin
- flipping the coin twenty more times
- taping a weight to one side of the coin
- flipping the coin over a smoother surface

Could you tell me which one is correct?

flipping the coin twenty more times