A teacher has a bag of marbles. There are 6 red, 6 blue, 8 green, 7 purple, and 8 yellow marbles in the bag. As the students enter the classroom, they draw a marble and keep it. If the first student in the room draws a yellow, and the second draws
a purple, what is the probability that the third student will draw a yellow also?
33%
21%
20%
25%

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this