In a bag containing only blue, red and green marbles, all but 15 are blue, all but
13 are red and all but 12 are green. How many are red?
Choose the correct choice from the following options
A) 13	B) 7	C) 25	D) 20	E) 10
All but blue means number of marbles except blue..hence, let x be the red marble,y   be the green marble,z be the blue marble...   x+y=15   y+z=13   x+z=12   solving this eqns, we get x=7 y=8 z=5 hence number of red marbles are 7   ANSWER:7
<result>B</result>
In a bag containing only blue, red and green marbles, all but 15 are blue, all but
13 are red and all but 12 are green. How many are red?