A mechanic finds that 30% of his customers own foreign cars, and that 40% own dogs. Assuming that these events are independent, what percent of the customers have neither a foreign car nor a dog

Since the events are independent, 30% of his customers have neither a foreign car nor a dog.

Step-by-step explanation:

Let the total number of his customers = 100.

Since the events are independent,

customers with foreign cars + customers that own dogs + customers that have neither a foreign car nor a dog = 100.

But,

Customers with foreign cars = 30% = 30

Customers that own dogs = 40% = 40

Customers with neither foreign car nor dog  = x%

So that,

     30 + 40 + x = 100

       70 + x = 100

      x = 100 - 70

      x = 30

Customers with neither foreign car nor dog  = 30.

Converting this value to percentage,

             =   × 100                      

             = 30%.

Therefore, 30% of his customers have neither a foreign car nor a dog.