(1)原式=2/7*5/3+5/7*5/3
=5/3*(2/7+5/7)
=5/3
(2)原式=(11/15+11/20)*30/11
=11/15*30/11+11/20+30/11
=2+3/2
=7/2
(3)原式=4-125/1000*16
=4-1/8*16
=4-2
=2
(4)原式=3/8*4/15+375/1000*11/15
=3/8*4/15+3/8*11/15
=3/8*(4/15+11/15)
=3/8
(5)原式=7/10*12
=42/5
(6)原式=(7/6-2/5*5/4)*7/10
=(7/6-1/2)*7/10
=2/3*7/10
=7/15