A bag contains yellow, green, blue, and white marbles. The ratio of yellow, green, blue, and white marbles is 1:2:3:4. If the bag contains 180 marbles, then how many blue marbles are there?

ratio of yellow, green, blue, and white marbles is 1:2:3:4, so ratio of blue marbles to total marbles is 3:(1+2+3+4)=3:10

x: the total number of blue marbles

3/10 = x/180

multiplying both sides by 180,

x = 54