If 20 coins are tossed, find the probability that they'll all land on tails.

The probability would be split for this problem cause knowing with 20 coins , you can split that even amount ... here's what I would do..

Michelle has 20 coins , but only half of them land on heads and others on tails

As for a half , halves are always equaling to 1/2 or 50 (%)  knowing we have 20 , you can evenly split that number of coins in a equal position

So ask your self .. what is half of 20? hmmm .. oh I got it , its 10! so knowing you have 20 but then later you split into half which is 10 ... meaning and knowing you have a 50% probability of getting the 20 coins hitting onto tails

hope this helps!