3: ⑴ 100∶5000
=1∶50
⑵ 100∶(100+5000)
=100∶5100
=1∶51
4: 5∶125=1∶25
10∶240=1∶24
6∶150=1∶25
4∶80=1∶20
第四杯最浓,第一杯和第三杯一样。
5: 略
6: (25×10÷2)∶(25×16)
=(25×5)∶(25×16)
= 5∶16
7: 2, 3, 5, 8, 13, 21, 34, (55), (89),.....
2:5≈0.667 3:5=0.6 5:8=0.625 8:13≈0.615 13:21≈0.619 21:34≈0.617 34:55≈0.618 55:89≈0.618规律:比值越来越接近0.618