Here is a question:
There are $140$ students in a batch. $10$ reserved stalls at the spring festival, $20$ sang on the stage and $45$ played games at various stalls. $8$ had reserved a stall and sang on the stage, $14$ sang and played games, $5$ who played games also had stalls reserved on their names. $2$ had stalls, sang and played games. How many did not go to the spring festival?
I tried to solve the problem with the Venn diagram but a set (people who just reserved stalls) is coming out to be $-1$. Can anyone help me out why?