[10-55分之7x1]+[9-55分之7x2]+[8-55分之7x3].+[1-55分之7x10]
=10+9+8+7+6+5+4+3+2+1-(1+2+3+4+5+6+7+8+9+10)*(7/55)
=55-55*(7/55)
=55-7
=48