1. Checking for divisibility by 3.

• 123456789 > 1+2+3+4+5+6+7+8+9 = 45 is divisible by 3.
  123456789 is also divisible by 3.
• 4327384926 > 4+3+2+7+3+8+4+9+2+6 = 48 is divisible by 3 .
  4327384926 is also divisible by 3 .
• 7777777777 > 7+7+7+7+7+7+7+7+7+7 = 70 is not divisible by 3.
  7777777777 is also not divisible 3.

2.Checking for divisibility by 11

• 308 > 3+08 is divisible by 11.
  308 is also divisible 11.
• 453825 > 45+38+25 = 108 is not divisible by 11.
  453825 is not also divisible 11.
• 187869 > 18+78+69 = 165 is divisible by 11.
  187869 is also divisible by 11.

3.Checking for divisibility by 909.

• 46385600 > 46+385+600 = 1031 is not divisible by 909 > 9+09 = 18.
  46385600 is not also divisible by 909.
• 36369999 > 36+369+999 = 1404 is divisible by 909 > 9+09 = 18.
  36369999 is also divisible by 909.
• 4072320 > 4+072+320=396 is divisible by 909 > 9+09 = 18.
  4072320 is also divisible by 909.

4.a 3,9,11,15.
4.b don't now.

1. I don't know.