(13 + 20) + 15 = 13 + (20 + 15)
Equations is what you have to do
Choosing blue or red: 3 blue + 4 red = 7 marbles
3 blue + 2 green + 4 red + 1 yellow = 10 marbles
Probability blue or red marble: 7/10
Choosing a marble that isn't blue or red: 2 green + 1 yellow = 3 marbles
Total marbles: 3 blue + 2 green + 4 red + 1 yellow = 10 marbles
Probability non-blue or red marble: 3/10
Answer:
or 
Step-by-step explanation:
Convert the mixed numbers into improper fractions.

Since the two fractions have the same denominator, just subtract the numerators.

If required, rewrite the fraction in simplest form.
