Riku's puzzle

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Across
  1. 4. 夏
  2. 6. happy and interesting
  3. 9. the word used for addition
  4. 10. the word used for division
  5. 11. the word used for multiplication
Down
  1. 1. to be able to take care of something
  2. 2. 友達
  3. 3. the word used for subtraction
  4. 5. 水
  5. 7. choices to choose from
  6. 8. fast and short