Abag contains red and blue marbles. given that 17/20 of the marbles are red, what percent of the marbles are blue?

The roots of the word percent translate roughly to "for each 100." If we have 3% of something, it's equivalent to saying we have 3/100 of that thing. What this means is that finding a percent of something is the same thing as finding a fraction of that thing, and then changing its denominator to 100.

Here, we'll find the fraction of blue marbles in the bag first. If red marbles take up 17/20 of the total marbles, we know that the remaining 3/20 must be blue. To find out what percentage that corresponds to, we'll need to convert 3/20 into an equivalent factor with a denominator of 100. We don't know what will be in the numerator yet, so we'll call that x:



To find x (our percentage), we can simply multiply both sides of our equation by 100 to get



So, the blue marbles take up 15% of the total number of marbles.