There are 130 red, blue and green marbles in a bag. The ratio of red to blue to green is 5:3:2 respectively. How much marbles in the bag are blue?

5 parts are red

3 parts are blue

2 parts are green

There are 10 parts in the bag altogether, and they add up to 130 marbles.

So each 'part' is 13 marbles.

Red = 5 parts = 65 marbles

Blue = 3 parts = 39 marbles

Green = 2 parts = 26 marbles

65 + 39 + 26 = 130 so we ended up on the track.

One would take the ratios, and add them.

5+3+2 = 10

The divide the total number of marbles by the sum of the ratios.

130/10 = 13

And finally multiply the quotient by each of the three numbers in the ratio (5:4:3) to get the number of marbles that are each colour.

Red: 13 * 5 = 65

Blue: 13 * 4 = 52

Green: 13 * 3 = 39

Therefore, there are 52 blue marbles in the bag.