Ken had a number of colored marbles in a bag. 1/4 of the marbles were red, 2/3 of the marbles were blue, and the rest were yellow. given that there were 120 red and yellow marbles all together, how many marbles were there in the bag

Red = 1/4
Blue = 2/3
Yellow= ?

First you will need to find how much of the fraction is yellow so:
RED= 1/4 = 3/12
BLUE= 2/3 = 8/12
YELLOW= add 3/12 with 8/12= 11/12
12/12 - 11/12= 1/12

so the yellow marbles are 1/12

yellow + red = 120
1/12    + 3/12= 120
4/12= 120

so 4/12 of the marbles are 120

how much is 8/12?
120 x 2= 240

now: 
red + yellow = 120
blue= 240

how many are in the bag? 120 + 240 = 360

360

I don't know if this is correct. but I tried. hope this helped:)

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put like terms together.orremember that the 45 becomes negative when moved to the other side.orthe minuses cancel out.