A kind of milk powder marked "Quality: 500 ± 5 grams" on the packaging bag. The quality inspector randomly inspected five bags, and the masses were 490 grams, 504 grams, 497 grams, 503 grams, and 492 grams. How many bags are the quality substandard?
一种在包装袋上标有"质量：500±5克"的奶粉，质检员抽检了五袋，质量分别是490克，504克，497克，503克，492克．其中质量不达标的有多少袋．
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