Mark has a bag that contains exactly 3 black marbles, 6 gold marbles, 2 purple
marbles and 6 red marbles.
Mark finds a number of white marbles and adds them to the bag. He tells Sam
that if she now draws a marble at random from the bag, the probability of it
being black or gold is 3
7
.
How many white marbles did Mark add to the bag?
+118654 
