A made-up survey of 100 students counts who learns French, German or Spanish…

Step 1. At least one. $40 + 30 + 25 - 10 - 8 - 6 + 3 = 74$ students. The $3$ students in all three were added three times and taken away three times, so they are added back once.

Step 2. None. $100 - 74 = 26$ students, so $P(\text{none}) = 0.26$.

Step 3. Exactly one. French only: $40 - 10 - 8 + 3 = 25$. German only: $30 - 10 - 6 + 3 = 17$. Spanish only: $25 - 8 - 6 + 3 = 14$. The total is $56$, so $P = 0.56$.