Explanation

This question asks us to relate parts to the whole using both total numbers and percentages. The long way to answer this question would be to calculate how many green marbles 25% represents, how many blue marbles 30% represents, then subtract this number from 80 and convert the number found to a percentage.

However, there is a much quicker route to the answer available. If we see that the bag is entirely composed of green, blue, and red marbles and 55% of the bag is made up of green and blue marbles, then consequently, the remaining marbles, all of which are red, must be equal to 45%.

This can be expressed as such:

25 + 30 + x = 100

x = 100 − 25 − 30

x = 100 − 55

x = 45

**The correct answer is (B).**

However, there is a much quicker route to the answer available. If we see that the bag is entirely composed of green, blue, and red marbles and 55% of the bag is made up of green and blue marbles, then consequently, the remaining marbles, all of which are red, must be equal to 45%.

This can be expressed as such:

25 + 30 + x = 100

x = 100 − 25 − 30

x = 100 − 55

x = 45