Final answer:
To find the number of people who attended the exam, you need to find the total number of candidates who were selected for the post of senior officer. From the given information, you can set up an equation and solve for the number of people who attended the exam, which is 15750.
Step-by-step explanation:
To find the number of people who attended the exam, you need to find the total number of candidates who were selected for the post of senior officer.
Let's assume that the total number of candidates who attended the exam is 'x'.
From the given information, 20% of the total candidates were qualified, which means 0.2x candidates qualified for the post.
Out of the qualified candidates, 10% were selected. So, 0.1(0.2x) candidates were selected for the post.
According to the question, the number of selects for the post of senior officer was 315.
Therefore, the equation is 0.1(0.2x) = 315.
Solving this equation, we get x = 15750.
So, 15750 people attended the exam.