Question

A box contains 14 large marbles and 10 small marbles. Each marble is either green or white. 9 of the large marbles are green, and 3 of the small marbles are white. If a marble is randomly selected from the box, what is the probability that it is large or green? Express your answer as a fraction or a decimal number rounded to four decimal places.

can you please explain the subtracting part, this is the part that I always get wrong

Answer 1

Number of green and large marbles = 9

Number of white and large marbles = 14 - 9 = 5

Number of white and small marbles = 3

Number of green and small marbles = 10 - 3 = 7

Total number of marbles = 9 + 5 + 3 + 7 = 24

Total number of green marbles = 9 + 7 = 16

Total number of large marbles = 9 + 5 = 14

If a marble is randomly selected from the box, the probability that it is large or green

= P( a randomly selected marble is large) + P( a randomly selected marble is green) - P( a randomly selected marble is large and green)