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Six-digit numbers are to be formed using the digits 3 4 5 6 7 9. If each digit can only be used once, what is the largest of these numbers divisible by 11?

User Mlvljr
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1 Answer

4 votes

Answer:

975634

Explanation:

You want the largest possible multiple of 11 that can be made from the digits 3,4,5,6,7,9.

Divisibility by 11

A number will be divisible by 11 if the difference between the sum of its even digits and the sum of its odd digits is a multiple of 11. For a 6-digit number, the sum of 3 of the digits must differ from the sum of the other 3 by 0 or 11.

Sums

The sum of all of the given digits is 34, an even number. If we can divide the set of digits into groups of 3 that each total 17, then we can form the required number. (There is no way to form groups whose sums differ by 11.)

The number 9 must be in one of the groups, so the other two numbers in that group must total 8. The only such pair is 5 and 3.

The first digit will be 9, and alternate digits after that will be 5 and 3. The remaining digits are 7, 6, and 4. Putting these in decreasing order will give the largest number:

975634 = 11×88694

The largest number divisible by 11 is 975634.

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User Kooskoos
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