脱式计算：①1214+35×114②（2.9+3.1）×313-257③215×57-57÷123．

Question

脱式计算：
①12 (1)/(4) + (3)/(5) × 1(1)/(4)
②（2.9+3.1）× 3(1)/(3) -2 (5)/(7)
③2 (1)/(5) × (5)/(7) - (5)/(7) ÷1(2)/(3) ．

Answer 1

①12 (1)/(4) + (3)/(5) × 1(1)/(4)
=12 (1)/(4) + (3)/(5) × (5)/(4) ，
=12 (1)/(4) + (3)/(4) ，
=13；

②（2.9+3.1）× 3(1)/(3) -2 (5)/(7)
=6× (10)/(3) -2 (5)/(7) ，
=20-2 (5)/(7) ，
=17 (2)/(7) ；

③2 (1)/(5) × (5)/(7) - (5)/(7) ÷1(2)/(3) ．
=2 (1)/(5) × (5)/(7) - (5)/(7) × (3)/(5) ，
=（ (11)/(5) - (3)/(5) ）× (5)/(7) ，
= (8)/(5) × (5)/(7) ，
= (8)/(7) ．