【Solution】Solution: 1 apple's mass + 2 pears' mass $=1600$ grams $\cdots$ (1), 3 apples' mass + 2 pears' mass $=2800$ grams…(2), 
(2) - (1) can get:
$3-1$ apples' mass $=2800-1600$
2 apples' mass $=1200$
1 apple's mass $=600$
Answer: 1 apple's mass is 600 grams.
Therefore, the answer is: 600.
8. (6 points) Look at the picture and fill in the numbers



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