JEE MainMathematicsSequences and SeriesNumerical+4 / −1
The sum of all 3-digit numbers less than or equal to 500, that are formed without using the digit "1" and they all are multiple of 11, is .
Numerical answer
View written solutionFree
Correct answer: 7975
- Divisibility rule for 11
For a 3-digit number , the number is divisible by if Since are digits and the number is at most , we will list valid numbers directly.
- Allowed digits
- The number is 3-digit, so the hundreds digit .
- Digit is not allowed.
- Number must be , so .
- Other digits can be from .
- Form of 3-digit multiples of 11
A 3-digit multiple of has the form: up to .
- Remove numbers containing digit
From the above list, exclude all numbers having digit : Also contains digit , so exclude it too.
Thus the valid numbers are:
- Add them
Let us sum carefully: [ \begin{aligned} &209+220+231+242+253+264+275+286+297 \ &= 2277 \end{aligned} ]
[ \begin{aligned} &308+330+352+363+374+385+396+407+429+440+462+473+484+495 \ &= 5698 \end{aligned} ]
So total sum is
- Final answer
The required sum is
- Comparison with stored answer
Stored correct answer is , but the correct computed sum is . Hence, I do not agree with the stored answer.
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