Library / CEMC Gauss (Grade 7) /349 of 462

CEMC Gauss (Grade 7), 2002

Algebra Difficulty 2.0 Junior Find the answer Canada

Mark has a bag that contains 3 black marbles, 6 gold marbles, 2 purple marbles, and 6 red marbles. Mark adds a number of white marbles to the bag and tells Susan that if she now draws a marble at random from the bag, the probability of it being black or gold is $\frac{3}{7}$ . The number of white marbles that Mark adds to the bag is

(A) $5$ (B) $2$ (C) $6$ (D) $4$ (E) $3$

We don't reproduce this publisher's solutions. Their own solution is here — work the problem first.

Want a route through all this instead of an archive? The track puts 2,604 problems in a working order, from Junior Challenge level to the IMO shortlist.

Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project. Solutions are the publisher's, linked not copied.