Rational numbers

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123456
Across
  1. 3. repeated addition
  2. 5. a×b=b×a
  3. 6. a number has no reciprocal
Down
  1. 1. (a×b)×c=a×(b×c)
  2. 2. a number has the reciprocal itself
  3. 4. the reciprocal of ___ is fivebyfour