(1)8080×1.25
=(8000+80)×1.25
=8000×1.25+80×1.25
=10000+100
=10100;
(2)([1/6+
1
8+
1
12])×24
=[1/6]×24+[1/8]×24+[1/12]×24
=4+3+2
=9;
(3)[2/15]÷([19/21+
3
7])×[1/2]
=[2/15]÷[4/3]×[1/2]
=[1/10]×[1/2]
=[1/20];
(4)[2/3]+([4/7+
1
2])×[7/25]
=[2/3]+[15/14]×[7/25]
=[2/3]+[3/10]
=[29/30].