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Let MM be the set of positive integers less than or equal to 20002000 such that the difference of any two numbers in MM is neither 55 nor 88. find the maximum numbers of elements in MM

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Q. Let MM be the set of positive integers less than or equal to 20002000 such that the difference of any two numbers in MM is neither 55 nor 88. find the maximum numbers of elements in MM
  1. Pick Smallest Integer: Let's start by picking the smallest positive integer, which is 11, and add it to set MM.
  2. Add Numbers to Set: Now, we can't add 1+5=61+5=6 or 1+8=91+8=9 to MM because the difference between these numbers and 11 is either 55 or 88. So, the next number we can add is 1+6=71+6=7.
  3. Identify Pattern: Continuing this pattern, we can't add 7+5=127+5=12 or 7+8=157+8=15 to MM, so the next number we can add is 7+6=137+6=13.
  4. Calculate Number of Elements: We notice a pattern: we can add a number to MM every 66th integer to avoid differences of 55 or 88. So, we can calculate the number of elements by dividing 20002000 by 66.
  5. Check Inclusion of Last Numbers: Dividing 20002000 by 66 gives us 2000/6=3332000/6 = 333 with a remainder of 22. So, we can have 333333 elements, and we need to check if we can include the last two numbers, 19991999 and 20002000.
  6. Verify First and Last Numbers: Since 19991994=51999 - 1994 = 5 and 20001992=82000 - 1992 = 8, we can't include 19991999 or 20002000 in MM. So, we stick with 333333 elements.
  7. Verify First and Last Numbers: Since 19991994=51999 - 1994 = 5 and 20001992=82000 - 1992 = 8, we can't include 19991999 or 20002000 in MM. So, we stick with 333333 elements. However, we need to check if the first and last numbers in our set follow the rule. The last number we can include is 1+333×6=19991 + 333 \times 6 = 1999, but we just determined we can't include 19991999.

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