Income tax computaion, prob with Saving Income!

Non-saving income taxation rates is

1-34370 pound – 20%
34371-150000 pond – 40%

right?

Ok, but when it comes to “Saving income” i saw, in several exam ans it shows,

Savings
7,475 × 20% 1,495
4,525 × 40% 1,810
12,000

& in several exam ans it shows also in different ways,

Savings
20,000 @ 40% = 8,000
20,000 @ 50% = 10,000
40,000

?!??!?! dont get it
someone pls help