To solve this question, the user needs to know how to find the average of a set of numbers and how to work with consecutive numbers.
The average of a set of numbers is found by adding up all the numbers in the set and then dividing by the total number of numbers.
For a set of consecutive numbers, the average of the set is equal to the middle number.
To find the difference between the averages of the first and last 10 numbers, we need to find the average of the first 10 numbers and the average of the last 10 numbers, and then subtract the former from the latter.
Let's represent the first number by x. Then, the next 29 consecutive numbers will be x+1, x+2, x+3, ..., x+28, x+29.
The average of the first 10 numbers will be the middle number of the set of the first 10 numbers. Since there are 10 numbers, the middle number will be the 5th number. Therefore the average of the first 10 numbers will be:
$$\frac{x + (x+1) + (x+2) + ... + (x+8) + (x+9)}{10} = x + 4.5$$
Similarly, the average of the last 10 numbers will be the middle number of the set of the last 10 numbers. Since there are 10 numbers, the middle number will be the 25th number. Therefore the average of the last 10 numbers will be:
$$\frac{(x+20) + (x+21) + (x+22) + ... + (x+27) + (x+28) + (x+29)}{10} = x + 24.5$$
The difference between the averages of the first and last 10 numbers will be:
$$(x+24.5) - (x+4.5) = 20$$
Therefore, the answer is:
The Answer is: D. 20.