（3）3.875×2.5+6.15×2.5
=2.5（3.875+6.15）
=2.5×10.025
=25.0625
（4）1/2×6+7/6×1/2
=1/2(6+7/6)
=1/2×43/6
=43/12
（5）5/6×84-2/7×84-1/4×84
=70-24-21
=45
望采纳!谢谢!