64x15+64x25 =64×（15+25）=64×40=2560 4243-854-146=4243-（854+146）=4243-1000=3243 6300 ÷25÷4 3 .8x9.9+3.8x0.1 =3.8×（9.9+0.1）=3.8×10=38 7 /16x10+7/16x6 =7/16×（10+6）=7/16×16=7 (2/3+7/5-2/1)...