=39*[(149-1)/149]+86*(149-1)]/149+16*3*49/149
=39*[1-1/149)+86*(1-1/149)+16*(149-2)/149
=39-39/149+86-86/149+16*(1-2/149)
=(39+86)-(39/149+86/149)+16-32/149)
=(39+86+16)-[(39+86+32)/149
=141-(149+8)/149
=141-1-(8/149)
=140-(8/149)
=139+(141/149
=139又149分之141
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