A box contains only red and blue balls. What is the probability of drawing a red ball from the box?

✓ Correct Answer: Option A

(1) Let R be red balls, B be blue. B=2R. P(red)=R/(R+B)=R/(R+2R)=R/3R=1/3. Sufficient. (2) (R-1)/(R-1+B)=2/5. This is one equation with two unknowns (R and B), so not sufficient alone.