Answer is P(1)+P(2)+P(3)+P(4)
A boy has 6 red and 7 blue blocks.
(i) in how many ways can he choose randomly 4 blocks.
i got 715 ways
(ii)what is the probablity that he will chose for red blocks.
i got 15/715 but i think is wrong.
(iii) what is the probability that the choice includes at least one blue block
Why do you think your answer is wrong??
It was ok to be suspicious, however
You get the same answer by summing the individual cases.
the purpose of the question is for you to discover that there is a fast way to calculate (iii)
At least 1 is blue is equivalent to "the 4 are not all red".
Since all probabilities sum to 1,
the answer is