We take 2 marbles from 20 marbles and the total ways is 20x19:2=190 But we need only 2 red marbles and the ways is 14x13:2=91 And finally we do the division 91:190=91/190 is the probability we need
Cavalieri's principle states that if two solids of equal height have equal cross-sectional areas at every level parallel to the respective bases, then the two solids have equal volume.
