Algebra
posted by Lacey on .
A box contains 15 blue marbles, 25 yellow marbles, 20 green marbles and 40 red marbles. How many ,arbles must you select to be sure that a green marble has been chosen ?

Since you can pick 15+25+40=80 marbles and get no greens, you must pick 81 to be sure that at least one is green.