# Thread: Understanding the contex of a question

1. ## Understanding the contex of a question

You have circular disc of diameter and weight the same as a 10 pence piece, you flick it up to 100 times and end up with 35 tails, if a percentage figure given is very low, how would you decide what that pecentage means?

2. ## Re: Understanding the contex of a question

it depends what you want to invesigate.

You have observed that the coin landed on tails less than half the time. An obvious investigation would be to see if this could be due to random chance (ie, the real probability is 50% and you just got unlucky), or if it suggests that the real probability of landing tails-up is less than 50%.

So you would do a hypothesis test to see if your results are significantly different from a 50/50 split.

The hypothesis test could be based on the binomial distribution but with 100 samples you would want to use a normal approximation, unless you are allowed to use a computer.

Spoiler:

the chance of getting 35 or fewer tails if the disc is fair is tiny (<0.02%) so you have extremely strong evidence that the true probability is not 50%.