Technically there is no way to answer this question, it says that 120 ADULTS were surveyed and then asks how many STUDENTS rank themselves as introverts. But if we a supposed to assume that all adults are students:
The ratio of 3:7 means that for every 3 introverts, there are 7 extroverts.
In other words for every 10 people (total introvert+extrovert) there are 3 introverts.
So to find the number of introverts in the group of 120, just multiply by 3/10 or 0.3
