The ratio of yellow balloons to blue balloons is 8:12
Then there are 100 balloons. Making the equation, we are able to have:
8X + 12X = 1000
20x = 1000
X = 50.
Yellow balloons = 8x = 8 50 = 400 yellow balloons
Blue balloons = 12X = 12 50 = 600 blue balloons
So there are 400 yellows balloons.