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in Permutations and combinations by (25 points)
The total number of six digit numbers formed using only the digits 4, 5, 9, which are divisible by 7 are p and The total number of six digit numbers formed using only the digits 4, 5, 9, which are divisible by q are 11 so find p + q

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1 Answer

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For q, the total number of six-digit numbers formed using only the digits 4, 5, 9, which are divisible by q=11, let's recheck the alternating sum of the digits:

  • Alternating sum of digits in the units place, hundreds place, and ten-thousands place: 4−5+9=84−5+9=8
  • Alternating sum of digits in the tens place, thousands place, and hundreds-of-thousands place: −4+5−9=−8−4+5−9=−8

The difference between these two sums is 8−(−8)=168−(−8)=16. This is not divisible by 11. So, q=0.

Now, for p, the total number of six-digit numbers formed using only the digits 4, 5, 9, which are divisible by 7, let's recheck the divisibility of the last three digits:

  • 459 (not divisible by 7)
  • 495 (not divisible by 7)
  • 549 (not divisible by 7)
  • 594 (not divisible by 7)
  • 945 (not divisible by 7)
  • 954 (divisible by 7)

There is only 1 combination that is divisible by 7.

So, p=1×1×1×1=1.

Therefore, p+q=0+1=1.

The correct answer is p+q=1.

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