F6 英国税法 关于tax savings income，求教1！

是在计算Savings income tax时遇到了麻烦，计算这个时，书上是这么说的：savings income is taxed at 10% in the starting rate band. if savings income falls within the basic rate band it is taxed at 20%, Once income is above the higher rate threshold,it is taxed at 40%.

不知道怎么理解，我是这么理解的，如果这个类别的收入落在开始的rate band里的话，就用10%的税率，如果落在基础 rate band里的话，就用20%的税率，如果再高就用40%的。

但书上有这么几道题：1.Jules has a salary of 20000,business profits of 30000,net dividends of 6750 and building society interest of 3000 net.He pays gross charges of 2000.

答案：                                                          non-saving                                saving                             dividend                 total

               business profits                            30000

               earnings                                       20000

               dividends                                                                                                                                7500

               building society interest                                                                   3750

               less charges                                 (2000)

               STI                                                48000                                         3750                               7500                        59250

               less personal allowance                (5035)

               taxable income                              42965                                         3750                               7500                        54215

               income tax

               non savings income

               2150*10%

               31150*22%

               9665*40%

郁闷点：savings income

               3750*40%          不明白这里为什么用40%的税率，这个数字落在了最高档的那个范围了吗？虽然书后面解释了点，但跟没解释差不多。问题是这个starting rate band 和basic rate band 都是多少，书前面倒是说了，但有定语的，说得明白，是 For  non-saving income 的。另外，就算是用这个，那也说不过去，3750，应该落在31150这个范围内了吧？不明白，请高人知道，鞠躬，拜谢。                 

第二道题：Mary has trading income of 14000.She also receives building society interest of 6400 net,dividends of 1800(net),and pays a charge of 2500 each year.How much cash will she have available to spend in 2006/07?忽略主要问题，只看saving income tax的计算

答案:                                                           non-savings                     savings                    dividend                                total

                      trading income                      14000

                      building society interest                                                  8000

                      dividends                                                                                                       2000

                      less charge                            (2500)

                      STI                                         11500                               8000                       2000                                    21500

                      less personal allowance         (5035)

                      taxable income                        6465                                8000                       2000                                    16465

                      non-saving income

                      略

注意：           saving income

                     8000*20%                            ????? 为什么？不明白为什么这里就用20%的税率？请问，这个收入的税率到底怎么分啊？再次鞠躬，拜谢