=[(2²-1²)+(4²-3²)+(6²-5²)+……+(100²-99²)]/[(1+9)+(2+8)+……+10+(9+1)+(8+2)+……+(1+9)]
=[(2+1)(2-1)+(4+3)(4-3)+……+(100+99)(100-99)]/(10+10+……+10)
=(3+7+11+……199)/100
=[(3+199)×25]/100
=5050÷100
=50.5
=[(2²-1²)+(4²-3²)+(6²-5²)+……+(100²-99²)]/[(1+9)+(2+8)+……+10+(9+1)+(8+2)+……+(1+9)]
=[(2+1)(2-1)+(4+3)(4-3)+……+(100+99)(100-99)]/(10+10+……+10)
=(3+7+11+……199)/100
=[(3+199)×25]/100
=5050÷100
=50.5