Of 560 marbles in a bag, 65% are red and the rest are blue. after 28 red marbles are replaced with blue ones, how many blue marbles need to be added to the bag so that the 65% of all marbles are blue?

400 blue marbles.

Step-by-step explanation:

We have been given that of 560 marbles in a bag, 65% are red and the rest are blue.

Then, after replacement:

Let x blue marbles be added. So we can set up an equation as:

Upon cross multiplying our equation we will get,

Using distributive property

Therefore, 400 blue marbles needed to be added to the bag so that the 65% of all marbles are blue.