Explanation:

- The average of seven numbers is given as 20.

- The total sum of these seven numbers would be 20 times 7, which is 140.

- If you subtract 2 from each number, the total reduction from the sum is 2 times 7, which equals 14.

- This makes the new sum of the numbers 140 - 14 = 126.

- The new average would be the new sum (126) divided by 7, which is 18.

- Option 4: 18 is the correct answer.