The licence plates for vehicles registered in Delhi consist of 3 letters (of English alphabet) followed by 1,2,3 or 4 digits. The letter on the extreme right has to be 'D'. For the 1-digit number plates, the number 0 is not allowed. For other, the digits and the letters, of course can repeat, but the numbers should be significant. Determine the possible number of licence plates.

Answer

To determine the total number of license plates for vehicles registered in Delhi, we need to consider the structure of the plates, which consists of 3 letters followed by 1, 2, 3, or 4 digits. The letter on the extreme right must be 'D', and there are specific rules regarding the digits. Let's break down the solution step by step.

### Step 1: Determine the letters
The license plate consists of 3 letters, with the last letter fixed as 'D'. Therefore, we only need to determine the first two letters.

- The total number of letters in the English alphabet is 26.
- The first two letters can be any of the 26 letters.

Thus, the number of ways to choose the first two letters is:
\[ 26 \times 26 = 676 \]

### Step 2: Determine the digits for each case
We will consider four cases based on the number of digits (1, 2, 3, or 4 digits).

#### Case 1: 1-digit number plate
- The only digit allowed is from 1 to 9 (0 is not allowed).
- Therefore, there are 9 options for the digit.

The total combinations for this case:
\[ 676 \times 9 = 6084 \]

#### Case 2: 2-digit number plate
- The first digit can be any digit from 0 to 9 (10 options).
- The second digit can also be any digit from 0 to 9 (10 options).

The total combinations for this case:
\[ 676 \times 10 \times 10 = 67600 \]

#### Case 3: 3-digit number plate
- The first digit can be any digit from 0 to 9 (10 options).
- The second digit can also be any digit from 0 to 9 (10 options).
- The third digit can also be any digit from 0 to 9 (10 options).

The total combinations for this case:
\[ 676 \times 10 \times 10 \times 10 = 676000 \]

#### Case 4: 4-digit number plate
- The first digit can be any digit from 0 to 9 (10 options).
- The second digit can also be any digit from 0 to 9 (10 options).
- The third digit can also be any digit from 0 to 9 (10 options).
- The fourth digit can also be any digit from 0 to 9 (10 options).

The total combinations for this case:
\[ 676 \times 10 \times 10 \times 10 \times 10 = 6760000 \]

### Step 3: Total number of license plates
Now, we add the total combinations from all four cases:
\[ 6084 + 67600 + 676000 + 6760000 = 7432684 \]

### Final Answer
The total number of possible license plates is:
\[ \boxed{7432684} \]