Answer:
1/2
Explanation:
So we know that there is a total of 10 people.
5 of these have grey hair.
To find the chances of a somone having grey hair, we need to divide people with grey hair over total people:

This is the same division we use to find things such as percentage and ratio as well.
Now lets plug in our numbers and solve:

So half of the people have grey hair.
Or(in percentage):
The probability is 50% that someone will have grey hair.
Hope this hepls!