Explanation:

Let’s break it down:

- We're told: 43% are boys, and 28% of the girls wear white socks. We need the total percent of the group in white socks.

- Statement I: 20 boys wore non-white socks.

- But we don’t know the total number of boys, just how many wore non-white socks. No way to get actual percentages.

- Statement II: 17% of boys wore white socks.

- We know what percent of boys wore white socks, but not the number of girls or their proportion, and nothing about the color breakdown for them except that 28% of girls wore white socks.

- Alone, each statement doesn’t give you enough.

- Putting them together? Let’s see:

- We know 43% are boys, so girls are 57%.

- If 20 boys wore non-white socks, and 17% of boys wore white socks, can we fix the group size?

- Let total group = x. Boys = 0.43x

- # of boys wearing white socks = 0.17 × 0.43x

- # of boys not in white socks = 0.43x - 0.17 × 0.43x = 0.83 × 0.43x = 20

- Now we can solve for x (total group size), then get # girls, then find percent with white socks using info about girls and boys.

What this really means is:

- Both statements together get you all the numbers you need.

- Alone, neither gives enough.

Correct option: Option 3