We will start with the easy ones:
First question:
5+7=

  12
  15
  10

How much is:
16+18=

  24
  34
  44

How much is:
60x5=

  5
  605
  300

Solve this:
800-(600+200)=

  800-800=000
  800-600+200=400
  Stupid!

How much is:
5x9=

  49
  42
  45

What is the oldest calculative operation?

  Subtraction
  Multiplication
  summation

How much is 1000 000-600 000+599 999=

  300 000+599 999=899 999
  400 000+599 999=999 999
  500 000+599 999=1099 999

Summation of numbers 643 659 and 356 341 reduce for 1!
Which one of these are correct?

  (643 659+356 341)-1=999 999
  (643 659+356 341)-1=1000 000-1=999 999
  (643 659+356 341)-1=(643 659-1)+356 341=643 658+356 341=999 999

How much is 1+1=

  2
  2
  2