①99999×7778+33333×66666②3.6×25.4+37.9×6.4③112-56+712-920+930-1342④54×17.6+36÷45+2.64×12.5．

Question

①99999×7778+33333×66666
②3.6×25.4+37.9×6.4
③ 1(1)/(2) - (5)/(6) + (7)/(12) - (9)/(20) + (9)/(30) - (13)/(42)
④ (5)/(4) ×17.6+36÷ (4)/(5) +2.64×12.5．

Answer 1

①99999×7778+33333×66666
=99999×7778+33333×3×22222，
=99999×77778+99999×22222，
=99999×（77778+22222），
=99999×100000，
=9999900000；

②3.6×25.4+37.9×6.4
=3.6×25.4+（25.4+12.5）×6.4，
=3.6×25.4+25.4×6.4+12.5×6.4，
=3.6×25.4+25.4×6.4+12.5×8×0.8
=25.4×（3.6+6.4）+100×0.8，
=254+80，
=334；

③ 1(1)/(2) - (5)/(6) + (7)/(12) - (9)/(20) + (9)/(30) - (13)/(42)
= (3)/(1) - (3)/(2) + (5)/(2) - (5)/(3) + (7)/(3) - (7)/(4) + (9)/(4) - (9)/(5) + (9)/(5) - (9)/(6) + (13)/(6) - (13)/(7) ，
=3+（ (5)/(2) - (3)/(2) ）+（ (7)/(3) - (5)/(3) ）+（ (9)/(4) - (7)/(4) ）+（ (9)/(5) - (9)/(5) ）+（ (13)/(6) - (9)/(6) ）- (13)/(7) ，
=3+1+ (2)/(3) + (1)/(2) +0+ (2)/(3) - (13)/(7) ，
=3 (41)/(42) ；

④ (5)/(4) ×17.6+36÷ (4)/(5) +2.64×12.5
=1.25×17.6+36×1.25+26.4×1.25，
=（17.6+26.4+36）×1.25，
=80×1.25，
=100．