2*1/7+7*1/12+12*1/17+17*1/22
=2/7+7/12+12/17+17/22
=(1-5/7)+(1-5/12)+(1-5/17)+(1-5/22)
=4-5(1/7+1/12+1/17+1/22)
=4-5[29/(7*22)+29/(12*17)]
=4-145(1/154+1/204)
=4-145[(102+77)/(77*2*102)]
=4-25955/15708
=2又5461/15708