3.8+4.29+2.71+6.212.5—0.78—3.2212.8×99+12.81.25×3.2×2.512.6×101—12.638.5÷2.5÷0.46.7×10.16.5×1014.85×981.2×2.5+0.8×2.528×17.5—28×7.54.8×12.56/7＋2/15＋1/7＋13/1519/21＋5/7...