Madison has a bag of 200 marbles. If twenty-two percent of her marbles are navy blue, 80 marbles are royal blue, 38% are baby blue, how many cobalt blue marbles does Madison have?

To make things easier, pretend she has 100 marbles and halve everything except for the percentages (everything will be doubled later).

If 22% of her marbles are navy, then 22 marbles are navy.
If 40 (half of 80) her marbles are royal blue, then 40% of her marbles are royal blue.
If 38% are baby blue, she has 38 baby blue marbles.

How many cobalt blue marbles does she have? Well, 22+40+38=100

Since we added the percentages, the ratio would be the same whether she has 100 or 200 marbles.

Since the percentages of navy, royal blue, and baby blue added up to 100%, she has no cobalt blue marbles.