Sixth grade mathematics solution

A The number of original books is 60 ÷ 2/3 = 90.

B The original number of books is 60 ÷ 2/5 = 150.

(60 represents the average score 120 copies, and the numbers are increased by a and b respectively, 2/3 of 3 represents the original proportion of A, and 2/5 of 5 represents the original proportion of B)

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