Ignoring for a second the strict gender binary here, let's break down what this problem is telling us. A ratio of 3 boys to 4 girls means that for every 3 + 4 = 7 students, 3 are boys and 4 are girls. A class of 28 students is 4 times bigger than 7, so we can multiply each number in the ratio by 4 to get the count for this larger class. Doing that math, we find 3 · 4 = 12 boys and 4 · 4 = 16 girls.
