At the art festival, the school held a calligraphy and painting exhibition. A total of 90 students from the fourth and fifth grades participated in the painting and calligraphy exhibition. How many students from the fourth and fifth grades participated in the calligraphy and painting exhibition? (Supplement the missing mathematical information, and then formulate the solution)
艺术节上，学校举行书画展，四、五年级共有90人参加，，四、五年级各有多少同学参加书画展？(补充缺少的数学信息，再列式解答)
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