Question

There are $5$ doors to a lecture hall. The number of ways that a student can enter the hall and leave it by a different door is

• A. $20$
• B. $16$
• C. $19$
• D. $21$

Answer 1

The correct option is A $20$

A student has 5 different doors to enter,
Every door a student enters through, there are 4 more doors to leave through.
So,
$\text{Total no. of ways}=5\times 4=20$