12.5×(36-七又五分之一)÷3.6 =12.5×(36-36/5)×10/36 =12.5×(36×10/36-36/5×10/36) =12.5×(10-2) =12.5×8 =100
①12.5×(36-7又5分之1)÷36
=12.5×36÷36-12.5×7又5分之1÷36
=12.5-2.5
=10
②45×2.08+1.5×37.6
=(15×3)×2.08+15×3.76
=15×(3×2.08)+15×3.76
=15×6.24+15×3.76
=15×(6.24+3.76)
=15×10
=150
(1+99)*99/2=4950 (首相+末项)*项数/2