(1)不知道
(2)
43×136／137+136×59／137+70×68／137
=43*136/137+136*59/137+35*136/137
=136*(43+59+35)/137
=136
(3)
999×778+333×666
=999×778+333×（3×222）
=999×778+333×3×222
=999×778+999×222
=999×（778+222）
=999×1000
=999000