2 heads or more in 3 coin toss formula what is the formula to calculate the probabilities of getting 2 heads or more in 3 coin toss ?
i've seen a lot of solution but almost all of them were using method of listing all of possible combination like HHT,HTH,etc
what i am trying to ask is the formula and/or method to calculate this using a formula and
no need to list all of the possible combination.
listing 3 coin toss combination is easy(8 possible combination),but suppose i change the coins to dice or say 20-side dice. that would take a long time to list all the possible combination.

The simplest is by symmetry.  The chance of at least two heads equals the chance of at least two tails, and if you add them you get exactly $1$ because one or the other has to happen.  Thus the chance is $\frac 12$.  This approach is not always available.
