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Find the sum of all four digit numbers that can be formed by the digits 1, 3, 5, 7, 9 without repetition.
  • a)
    666700
  • b)
    666600
  • c)
    678860
  • d)
    665500
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
Find the sum of all four digit numbers that can be formed by the digit...
To find the sum of all four-digit numbers that can be formed using the digits 1, 3, 5, 7, and 9 without repetition, we need to consider the possible arrangements of these digits.

Arranging the digits:
Since we are forming four-digit numbers, we need to select four digits out of the given five. The number of ways to do this is given by the combination formula:

C(n, r) = n! / (r!(n-r)!)

where n is the total number of items, and r is the number of items selected.

In this case, n = 5 (number of digits) and r = 4 (number of positions in a four-digit number). Therefore, the number of possible arrangements is:

C(5, 4) = 5! / (4!(5-4)!) = 5! / (4! * 1!) = 5

So, there are 5 possible arrangements of the digits.

Finding the sum:
To find the sum of all four-digit numbers, we need to consider each digit's position.

For each position, we have five options to choose from: 1, 3, 5, 7, and 9.

- Thousands place: Since the number cannot start with zero, we have four options for the thousands place (3, 5, 7, and 9).
- Hundreds place: After selecting the thousands digit, we have three options left for the hundreds place.
- Tens place: After selecting the thousands and hundreds digits, we have two options left for the tens place.
- Units place: Finally, we have one option left for the units place.

Therefore, the sum of all possible four-digit numbers is:

(3 + 5 + 7 + 9) * 3! * 2! * 1!

= (24) * (6) * (2) * (1)

= 288

However, this sum does not include the original numbers formed by the given digits (1357, 1375, 1537, 1573, etc.). So, we need to add these numbers to the sum:

1357 + 1375 + 1537 + 1573 + ...

To find this sum, we can observe that each digit appears in each position an equal number of times (as there are 5 digits and 4 positions). Therefore, the sum of these numbers can be calculated as:

(1 + 3 + 5 + 7 + 9) * (1111 + 1111 + 1111 + ...)

= 25 * (1111)

= 27775

Adding this to the previous sum, we get:

288 + 27775 = 28063

However, none of the given options match this answer. Therefore, there may be an error in the options provided.
Free Test
Community Answer
Find the sum of all four digit numbers that can be formed by the digit...
The given digits are 1, 3, 5, 7, 9
Sum of r digit number= n-1Pr-1
(Sum of all n digits)×(1111… r times)
N is the number of non zero digits.
Here n=5, r=4
The sum of 4 digit numbers
4P3 (1+3+5+7+9)(1111)=666600.
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Find the sum of all four digit numbers that can be formed by the digits 1, 3, 5, 7, 9 without repetition.a)666700b)666600c)678860d)665500Correct answer is option 'B'. Can you explain this answer?
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