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17/72-19/90+21/110-23/132
=(1/8+1/9)-(1/9+1/10)+(1/10+1/11)-(1/11+1/12)
=1/8+1/9-1/9-1/10+1/10+1/11-1/11-1/12
=1/8-1/12
=1/24