Final answer:
To find the number of white marbles in the bag, set up a proportion using the given ratio and solve for the unknown variable. The number of white marbles is 38.
Step-by-step explanation:
To find the number of white marbles in the bag, we need to determine the ratio of blue marbles to white marbles. According to the information given, there are 21 blue marbles for every 4 white marbles.
So, we can set up a proportion to solve for the number of white marbles: 21/4 = 200/x.
Cross-multiplying, we get 21x = 800. Dividing both sides by 21, we find that x, the number of white marbles, is 38.1.
Since we can't have a fraction of a marble, the closest whole number to 38.1 is 38. Therefore, there are 38 white marbles in the bag.