1/8+1/24+1/80+1/120
=1/8+(1/8)*(1/3)+(1/8)*(1/10)+(1/8)*(1/15)
=(1/8)*(1+1/3+1/10+1/15)
=(1/8)*(3/2)
=3/16
1/8+1/24+1/80+1/120
=30/240+10/240+3/240+2/240
=45/240
=3/16
1/8+1/24+1/80+1/120=1/4(1/2+1/6+1/20+1/30)
=1/4(1-1/2+1/2-1/3+1/4-1/5+1/5-1/6)
=1/4(1-1/3+1/4-1/6)
=1/4*3/4
=3/16
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