If a bag has 5 red marbles and 15 blue marbles, what fraction of the marbles are red?

If a bag has 5 red marbles and 15 blue marbles, what fraction of the marbles are red?

• A. 1/3
• B. 1/4
• C. 1/5
• D. 3/4

Answer: (B)

To find what fraction of the marbles are red, compare the number of red marbles to the total number of marbles. There are 5 red and 15 blue, so the total is 20. The fraction red is 5/20, which simplifies by dividing numerator and denominator by 5 to 1/4. That means one fourth of the marbles are red (25%). The other fractions don’t match 5 out of 20—for example, 1/3 would imply about 6.7 red marbles, 1/5 would be 4 red out of 20, and 3/4 would be 15 red out of 20.

To find what fraction of the marbles are red, compare the number of red marbles to the total number of marbles. There are 5 red and 15 blue, so the total is 20. The fraction red is 5/20, which simplifies by dividing numerator and denominator by 5 to 1/4. That means one fourth of the marbles are red (25%). The other fractions don’t match 5 out of 20—for example, 1/3 would imply about 6.7 red marbles, 1/5 would be 4 red out of 20, and 3/4 would be 15 red out of 20.