If 6 boys fill 6 notebooks in 6 weeks and 4 girls fill 4 notebooks in 4 weeks, how many notebooks will a class of 12 boys and 12 girls fill in 12 weeks?
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one child fill a notebook every week
so 24 children will fill 24 notebooks in 1 week
so 24 children will fill 24*12 = 288 notebooks in 12 weeks