can be computed by substituting these values in the formula:

An intuitive way to solve this is to assume the school has N students. Number of boys = 0.6N and number of girls = 0.4N. If N is large enough that rounding errors can be ignored, total number of trouser wearers = 0.6N + 50% of 0.4N. And number of girl trouser wearers = 50% of 0.4N. Therefore, in the population of trousers, girls are (50% of 0.4N)/(0.6N + 50% of 0.4N) = 25%. In other words, if you separated out the group of trouser wearers, a quarter of that group