Use three dice.

Have
a friend roll
the dice and then stack them one on top of the other.

Tell
your friend
that you can not see five
faces of the dice.

The
5
numbers you
cannot see are :

the
bottom of the
top dice

the
top of the
second dice

the
bottom of the
second dice

the
top of the
last dice

the
bottom of the
last dice

You
will now
predict the total of the five hidden
numbers.

In
your head
subtract the very top face of the three dice from 21.

The
answer will
be the total of the five hidden numbers.

In
the video, the
top number is 4,
therefore other five will add up to (21 - 4 = 17) 17

Ps:

You
can also do
this math trick with two dice. Simply subtract
the top
number from 14.

Watch
the video.